Problem: Fox Ciel is going to publish a paper on FOCS (Foxes Operated Computer Systems, pronounce: "Fox"). She heard a rumor: the authors list on the paper is always sorted in the lexicographical order. 

After checking some examples, she found out that sometimes it wasn't true. On some papers authors' names weren't sorted in lexicographical order in normal sense. But it was always true that after some modification of the order of letters in alphabet, the order of authors becomes lexicographical!

She wants to know, if there exists an order of letters in Latin alphabet such that the names on the paper she is submitting are following in the lexicographical order. If so, you should find out any such order.

Lexicographical order is defined in following way. When we compare s and t, first we find the leftmost position with differing characters: si ≠ ti. If there is no such position (i. e. s is a prefix of t or vice versa) the shortest string is less. Otherwise, we compare characters si and ti according to their order in alphabet.

Input

The first line contains an integer n (1 ≤ n ≤ 100): number of names.

Each of the following n lines contain one string namei (1 ≤ |namei| ≤ 100), the i-th name. Each name contains only lowercase Latin letters. All names are different.

Output

If there exists such order of letters that the given names are sorted lexicographically, output any such order as a permutation of characters 'a'–'z' (i. e. first output the first letter of the modified alphabet, then the second, and so on).

Otherwise output a single word "Impossible" (without quotes).

Examples

Input

3
rivest
shamir
adleman


Output

bcdefghijklmnopqrsatuvwxyz


Input

10
tourist
petr
wjmzbmr
yeputons
vepifanov
scottwu
oooooooooooooooo
subscriber
rowdark
tankengineer


Output

Impossible


Input

10
petr
egor
endagorion
feferivan
ilovetanyaromanova
kostka
dmitriyh
maratsnowbear
bredorjaguarturnik
cgyforever


Output

aghjlnopefikdmbcqrstuvwxyz


Input

7
car
care
careful
carefully
becarefuldontforgetsomething
otherwiseyouwillbehacked
goodluck


Output

acbdefhijklmnogpqrstuvwxyz

Solution (in JAVA):

Solution:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.NoSuchElementException;
import java.util.Random;
import java.util.Set;
import java.util.Stack;
import java.util.StringTokenizer;
import java.util.TreeMap;
import java.util.TreeSet;

// CFPS -> CodeForcesProblemSet
public final class CFPS {
	static FastReader fr = new FastReader();
	static PrintWriter out = new PrintWriter(System.out);
	static final int gigamod = 1000000007;
	static int t = 1;
	static double epsilon = 0.00000001;
	
	public static void main(String[] args) {
		OUTER: 
		for (int tc = 0; tc < t; tc++) {
			
			int n = fr.nextInt();
			String[] names = new String[n];
			for (int i = 0; i < n; i++)
				names[i] = fr.next();
			
			// Observations: 
			
			// 1. The sequence of letters in the alphabet will be determined
			// by the order of the strings in the array.
			
			// 2. We can find out, for this and the next string, the first 
			// position of difference and then, we can determine the order
			// of letters.
			
			// 3. If for any 'i', names[i+1] == names[i] for all indices but
			// names[i].length() > names[i+1].length(), the answer will be
			// impossible.
			
			LinkedHashSet<Point> lhs = new LinkedHashSet<>();
			
			for (int i = 0; i < n - 1; i++) {
				
				String thisName = names[i];
				String nextName = names[i + 1];
				
				int lenThis = thisName.length();
				int lenNext = nextName.length();
				
				int diffIdx = -1;
				for (int j = 0; j < Math.min(lenThis, lenNext); j++) {
					if (thisName.charAt(j) != nextName.charAt(j)) {
						diffIdx = j;
						break;
					}
				}
				
				if (diffIdx == -1) {
					if (thisName.compareTo(nextName) == 1) {
						out.println("Impossible");
						continue OUTER;
					}
					continue;
				}
				
				// The char in the first string is smaller than the char in 
				// the second string.
				Point p = new Point(thisName.charAt(diffIdx), nextName.charAt(diffIdx));
				lhs.add(p);
			}
			
			/*for (Point p : lhs)
				out.println((char) p.x + " " + (char) p.y);*/
			
			Digraph charsDG = new Digraph(26);
			for (Point p : lhs) {
				
				char fromChar = (char) p.x;
				char toChar = (char) p.y;
				
				charsDG.addEdge(fromChar - 97, toChar - 97);
			}
			
			Stack<Integer> topo = Digraph.topologicalSort(charsDG);
			StringBuilder ans = new StringBuilder();
			while (!topo.isEmpty()) {
				char topChar = (char) ((int) topo.pop() + 97);
				ans.append(topChar);
			}
			
			char[] ansChars = ans.toString().toCharArray();
			
			// Checking if the answer is valid.
			for (Point p : lhs) {
				
				char fromChar = (char) p.x;
				char toChar = (char) p.y;
				
				// Finding the indices in the answer.
				int fromIdx = -1, toIdx = -1;
				for (int i = 0; i < 26; i++) {
					if (ansChars[i] == fromChar)
						fromIdx = i;
					if (ansChars[i] == toChar)
						toIdx = i;
				}	
				
				if (fromIdx >= toIdx) {
					out.println("Impossible");
					continue OUTER;
				}
			}
			
			ans.append("\n");
			out.print(ans.toString());
		}
		out.close();
	}
	
	static String reverse(String s) {
		
		StringBuilder sb = new StringBuilder();
		int n = s.length();
		
		for (int i = n - 1; i > -1; i--) {
			sb.append(s.charAt(i));
		}
		
		return sb.toString();
	}
	
	static long power(long x, int y)
	  {
		// int p = 998244353;
		int p = gigamod;
	    long res = 1; // Initialize result
	 
	    x = x % p; // Update x if it is more than or
	    // equal to p
	 
	    if (x == 0)
	      return 0; // In case x is divisible by p;
	 
	    while (y > 0)
	    {
	 
	      // If y is odd, multiply x with result
	      if ((y & 1) != 0)
	        res = (res * x) % p;
	 
	      // y must be even now
	      y = y >> 1; // y = y/2
	      x = (x * x) % p;
	    }
	    return res;
	  }
	
	// Maps elements in a 2D matrix serially to elements in 
	// a 1D array.
	static int mapTo1D(int row, int col, int n, int m) {
		return row * m + col;
	}
	
	// Inverse of what the one above does.
	static int[] mapTo2D(int idx, int n, int m) {
		int[] rnc = new int[2];
		rnc[0] = idx / m;
		rnc[1] = idx % m;
		return rnc;
	}
	
	
	// Checks if s has subsequence t.
	static boolean hasSubsequence(String s, String t) {
		char[] schars = s.toCharArray();
		char[] tchars = t.toCharArray();
		int slen = schars.length, tlen = tchars.length;
		int tctr = 0;
		
		if (slen < tlen) return false;
		
		for (int i = 0; i < slen || i < tlen; i++) {
			if (tctr == tlen) break;
			if (schars[i] == tchars[tctr]) {
				tctr++;
			}
		}
		
		if (tctr == tlen) return true;
		return false;
	}
	
	// Returns the binary string of length at least bits.
	static String toBinaryString(long num, int bits) {
		StringBuilder sb = new StringBuilder(Long.toBinaryString(num));
		sb.reverse();
		for (int i = sb.length(); i < bits; i++)
			sb.append('0');
		return sb.reverse().toString();
	}
	
	static class CountMap extends TreeMap<Long, Integer>{
		
		CountMap() {
		}
		
		CountMap(CountMap cm) {
			
		}
		
		public void removeTM(Long key) {
			super.remove(key);
		}
		
		public void removeTM(Integer key) {
			super.remove((long) key);
		}
		
		public Integer put(Long key) {
			if (super.containsKey(key)) {
				return super.put(key, super.get(key) + 1);
			} else {
				return super.put(key, 1);
			}
		}
		
		public Integer put(int key) {
			if (super.containsKey((long) key)) {
				return super.put((long) key, super.get((long) key) + 1);
			} else {
				return super.put((long) key, 1);
			}
		}
		
		public Integer remove(Long key) {
			Integer count = super.get(key);
			if (count == null) return -1;
			if (count == 1)
				return super.remove(key);
			else
				return super.put(key, super.get(key) - 1);
		}
		
		public Integer remove(int key) {
			Integer count = super.get((long) key);
			if (count == null) return -1;
			if (count == 1)
				return super.remove((long) key);
			else
				return super.put((long) key, super.get((long) key) - 1);
		}
		
		public Integer get(int key) {
			Integer count = super.get((long) key);
			if (count == null)
				return 0;
			return count;
		}
		
		public Integer get(long key) {
			Integer count = super.get(key);
			if (count == null)
				return 0;
			return count;
		}
	}
	
	static class Point implements Comparable<Point> {
		long x;
		long y;
		int id;
		
		Point() {
			x = y = id = 0;
		}
		
		Point(Point p) {
			this.x = p.x;
			this.y = p.y;
			this.id = p.id;
		}
		
		Point(long a, long b, int id) {
			this.x = a;
			this.y = b;
			this.id = id;
		}
		
		Point(long a, long b) {
			this.x = a;
			this.y = b;
		}
		
		@Override
		public int compareTo(Point o) {
			if (this.x > o.x)
				return 1;
			if (this.x < o.x)
				return -1;
			if (this.y > o.y)
				return 1;
			if (this.y < o.y)
				return -1;
			return 0;
		}
		
		public boolean equals(Point that) {
			return this.compareTo(that) == 0;
		}
	}
	
	static class PointComparator implements Comparator<Point> {
		@Override
		public int compare(Point o1, Point o2) {
			
			long o1Len = o1.y - o1.x;
			long o2Len = o2.y - o2.x;
			
			if (o1Len > o2Len)
				return -1;
			
			if (o2Len > o1Len)
				return 1;
			
			if (o1.x > o2.x)
				return 1;
			
			if (o2.x > o1.x)
				return -1;
			
			return 0;
		}
	}
	
	// Returns the largest power of k that fits into n.
	static int largestFittingPower(long n, long k) {
		int lo = 0, hi = logk(Long.MAX_VALUE, 3);
		int largestPower = -1;
		while (lo <= hi) {
			int mid = lo + (hi - lo)/2;
			
			long val = (long) Math.pow(k, mid);
			if (val <= n) {
				largestPower = mid;
				lo = mid + 1;
			} else {
				hi = mid - 1;
			}
		}
		return largestPower;
	}
	
	static String bitSetToString(int set) {
		// We have to print all the elements that are present
		// in the set.
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < 30; i++) {
			if (((set >> i) & 1) == 1) {
				// The 'i'th bit is on meaning that the element 'i' is 
				// present in the set.
				sb.append((i + 1) + " ");
			}
		}
		sb.append("\n");
		return sb.toString();
	}
	
	static String displayBitSet(long set) {
		// We have to print all the elements that are present
		// in the set.
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < 60; i++) {
			if (((set >> i) & 1) == 1) {
				// The 'i'th bit is on meaning that the element 'i' is 
				// present in the set.
				sb.append((i + 1) + " ");
			}
		}
		sb.append("\n");
		return sb.toString();
	}
	
	static int addToBitSet(int set, int element) {
		set = (set) | (1 << (element - 1));
		return set;
	}
	
	static int removeFromBitSet(int set, int element) {
		// Checking whether the bit is present.
		if ((set & (1 << (element - 1))) == 0) return set;
		set = set ^ (1 << (element - 1));
		return set;
	}
	
	// Returns map of factor and its power in the number.
	static TreeMap<Long, Integer> primeFactorization(long num) {
		TreeMap<Long, Integer> map = new TreeMap<>();
		while (num % 2 == 0) {
			num /= 2;
			Integer pwrCnt = map.get(2L);
			map.put(2L, pwrCnt != null ? pwrCnt + 1 : 1);
		}
		
		for (long i = 3; i * i <= num; i += 2) {
			while (num % i == 0) {
				num /= i;
				Integer pwrCnt = map.get(i);
				map.put(i, pwrCnt != null ? pwrCnt + 1 : 1);
			}
		}
		
		// If the number is prime, we have to add it to the 
		// map.
		if (num != 1)
			map.put(num, 1);
		
		return map;
	}
	
	// Returns map of factor and its power in the number.
	static TreeMap<Integer, Integer> primeFactorization(int num) {
		TreeMap<Integer, Integer> map = new TreeMap<>();
		while (num % 2 == 0) {
			num /= 2;
			Integer pwrCnt = map.get(2);
			map.put(2, pwrCnt != null ? pwrCnt + 1 : 1);
		}
		
		for (int i = 3; i * i <= num; i += 2) {
			while (num % i == 0) {
				num /= i;
				Integer pwrCnt = map.get(i);
				map.put(i, pwrCnt != null ? pwrCnt + 1 : 1);
			}
		}
		
		// If the number is prime, we have to add it to the 
		// map.
		if (num != 1)
			map.put(num, 1);
		
		return map;
	}
	
	static Set<Long> divisors(long num) {
		Set<Long> divisors = new TreeSet<Long>();
		divisors.add(1L);
		divisors.add(num);
		
		for (long i = 2; i * i <= num; i++) {
			if (num % i == 0) {
				divisors.add(num/i);
				divisors.add(i);
			}
		}
		return divisors;
	}
	
	static void dfs(int node, boolean[] marked, ArrayList<Integer>[] adj) {
		if (marked[node]) return;

		marked[node] = true;
		for (int adjc : adj[node])
			dfs(adjc, marked, adj);
	}
	
	// Returns the index of the first element
	// larger than or equal to val.
	static int bsearch(int[] arr, int val, int lo, int hi) {
		int idx = -1;
		while (lo <= hi) {
			int mid = lo + (hi - lo)/2;
			if (arr[mid] >= val) {
				idx = mid;
				hi = mid - 1;
			} else
				lo = mid + 1;
		}
		return idx;
	}
	
	static int bsearch(long[] arr, long val, int lo, int hi) {
		int idx = -1;
		while (lo <= hi) {
			int mid = lo + (hi - lo)/2;
			if (arr[mid] >= val) {
				idx = mid;
				hi = mid - 1;
			} else
				lo = mid + 1;
		}
		return idx;
	}
	
	// Returns the index of the last element 
	// smaller than or equal to val.
	static int bsearch(long[] arr, long val, int lo, int hi, boolean sMode) {
		int idx = -1;
		while (lo <= hi) {
			int mid = lo + (hi - lo)/2;
			if (arr[mid] > val) {
				hi = mid - 1;
			} else {
				idx = mid;
				lo = mid + 1;
			}
		}
		return idx;
	}
	
	static int bsearch(int[] arr, long val, int lo, int hi, boolean sMode) {
		int idx = -1;
		while (lo <= hi) {
			int mid = lo + (hi - lo)/2;
			if (arr[mid] > val) {
				hi = mid - 1;
			} else {
				idx = mid;
				lo = mid + 1;
			}
		}
		return idx;
	}
	
	static long factorial(long n) {
		if (n <= 1)
			return 1;
		long factorial = 1;
		for (int i = 1; i <= n; i++)
			factorial = mod(factorial * i);
		return factorial;
	}
	
	static long factorialInDivision(long a, long b) {
		if (a == b)
			return 1;
		if (b < a) {
			long temp = a;
			a = b;
			b = temp;
		}
		
		long factorial = 1;
		for (long i = a + 1; i <= b; i++)
			factorial = mod(factorial * i);
		return factorial;
	}
	
	static BigInteger factorialInDivision(BigInteger a, BigInteger b) {
		if (a.equals(b))
			return BigInteger.ONE;
		return a.multiply(factorialInDivision(a.subtract(BigInteger.ONE), b));
	}
	
	static long nCr(long n, long r) {
		long p = gigamod;
	    // Base case
	    if (r == 0)
	        return 1;
	 
	    // Fill factorial array so that we
	    // can find all factorial of r, n
	    // and n-r
	    long fac[] = new long[(int)n + 1];
	    fac[0] = 1;
	    for (int i = 1; i <= n; i++)
	        fac[i] = fac[i - 1] * i % p;
	 
	    return (fac[(int)n] * modInverse(fac[(int)r], p) % p
	                    * modInverse(fac[(int)n - (int)r], p) % p) % p;
	}
	
	static long modInverse(long n, long p) {
	    return power(n, p - 2, p);
	}
	
	static long power(long x, long y, long p) {
	    long res = 1; // Initialize result
	 
	    x = x % p; // Update x if it is more than or
	    // equal to p
	 
	    while (y > 0) {
	        // If y is odd, multiply x with result
	        if ((y & 1)==1)
	            res = (res * x) % p;
	 
	        // y must be even now
	        y = y >> 1; // y = y/2
	        x = (x * x) % p;
	    }
	    return res;
	}
	
	static long nPr(long n, long r) {
		return factorialInDivision(n, n - r);
	}
	
	static int log2(long n) {
		return (int)(Math.log(n) / Math.log(2));
	}
	
	static double log2(long n, boolean doubleMode) {
		return (Math.log(n) / Math.log(2));
	}
	
	static int logk(long n, long k) {
		return (int)(Math.log(n) / Math.log(k));
	}
	
	// Sieve of Eratosthenes: 
	static boolean[] primeGenerator(int upto) {
		boolean[] isPrime = new boolean[upto + 1];
		Arrays.fill(isPrime, true);
		isPrime[1] = isPrime[0] = false;

		for (long i = 2; i * i < upto + 1; i++)
			if (isPrime[(int) i])
				// Mark all the multiples greater than or equal
				// to the square of i to be false.
				for (long j = i; j * i < upto + 1; j++)
					isPrime[(int) j * (int) i] = false;
		return isPrime;
	}

	static int gcd(int a, int b) {
		if (b == 0) {
			return a;
		} else {
			return gcd(b, a % b);
		}
	}
	
	static long gcd(long a, long b) {
		if (b == 0) {
			return a;
		} else {
			return gcd(b, a % b);
		}
	}
	
	static int gcd(int[] arr) {
		int n = arr.length;
		int gcd = arr[0];
		for (int i = 1; i < n; i++) {
			gcd = gcd(gcd, arr[i]);
		}
		return gcd;
	}
	
	static long gcd(long[] arr) {
		int n = arr.length;
		long gcd = arr[0];
		for (int i = 1; i < n; i++) {
			gcd = gcd(gcd, arr[i]);
		}
		return gcd;
	}
	
	static long lcm(int[] arr) {
		int lcm = arr[0];
		int n = arr.length;
		for (int i = 1; i < n; i++) {
			lcm = (lcm * arr[i]) / gcd(lcm, arr[i]);
		}
		return lcm;
	}
	
	static long lcm(long[] arr) {
		long lcm = arr[0];
		int n = arr.length;
		for (int i = 1; i < n; i++) {
			lcm = (lcm * arr[i]) / gcd(lcm, arr[i]);
		}
		return lcm;
	}
	
	static long lcm(int a, int b) {
		return (a * b)/gcd(a, b);
	}
	
	static long lcm(long a, long b) {
		return (a * b)/gcd(a, b);
	}
	
	static boolean less(int a, int b) {
		return a < b ? true : false;
	}
	
	static boolean isSorted(int[] a) {
		for (int i = 1; i < a.length; i++) {
			if (less(a[i], a[i - 1]))
				return false;
		}
		return true;
	}
	
	static boolean isSorted(long[] a) {
		for (int i = 1; i < a.length; i++) {
			if (a[i] < a[i - 1])
				return false;
		}
		return true;
	}

	static void swap(int a, int b) {
		int temp = a;
		a = b;
		b = temp;
	}
	
	static void swap(long a, long b) {
		long temp = a;
		a = b;
		b = temp;
	}
	
	static void swap(double a, double b) {
		double temp = a;
		a = b;
		b = temp;
	}
	
	static void swap(int[] a, int i, int j) {
		int temp = a[i];
		a[i] = a[j];
		a[j] = temp;
	}
	
	static void swap(long[] a, int i, int j) {
		long temp = a[i];
		a[i] = a[j];
		a[j] = temp;
	}
	
	static void swap(double[] a, int i, int j) {
		double temp = a[i];
		a[i] = a[j];
		a[j] = temp;
	}
	
	static void swap(char[] a, int i, int j) {
		char temp = a[i];
		a[i] = a[j];
		a[j] = temp;
	}
	
	static void sort(int[] arr) {
		shuffleArray(arr, 0, arr.length - 1);
		Arrays.sort(arr);
	}
	
	static void sort(char[] arr) {
		shuffleArray(arr, 0, arr.length - 1);
		Arrays.sort(arr);
	}
	
	static void sort(long[] arr) {
		shuffleArray(arr, 0, arr.length - 1);
		Arrays.sort(arr);
	}
	
	static void sort(double[] arr) {
		shuffleArray(arr, 0, arr.length - 1);
		Arrays.sort(arr);
	}
	
	static void reverseSort(int[] arr) {
		shuffleArray(arr, 0, arr.length - 1);
		Arrays.sort(arr);
		int n = arr.length;
		for (int i = 0; i < n/2; i++)
			swap(arr, i, n - 1 - i);
	}
	
	static void reverseSort(char[] arr) {
		shuffleArray(arr, 0, arr.length - 1);
		Arrays.sort(arr);
		int n = arr.length;
		for (int i = 0; i < n/2; i++)
			swap(arr, i, n - 1 - i);
	}
	
	static void reverseSort(long[] arr) {
		shuffleArray(arr, 0, arr.length - 1);
		Arrays.sort(arr);
		int n = arr.length;
		for (int i = 0; i < n/2; i++)
			swap(arr, i, n - 1 - i);
	}
	
	static void reverseSort(double[] arr) {
		shuffleArray(arr, 0, arr.length - 1);
		Arrays.sort(arr);
		int n = arr.length;
		for (int i = 0; i < n/2; i++)
			swap(arr, i, n - 1 - i);
	}
	
	static void shuffleArray(long[] arr, int startPos, int endPos) {
		Random rnd = new Random();
		for (int i = startPos; i < endPos; ++i) {
			long tmp = arr[i];
			int randomPos = i + rnd.nextInt(endPos - i);
			arr[i] = arr[randomPos];
			arr[randomPos] = tmp;
		}
	}
	
	static void shuffleArray(int[] arr, int startPos, int endPos) {
		Random rnd = new Random();
		for (int i = startPos; i < endPos; ++i) {
			int tmp = arr[i];
			int randomPos = i + rnd.nextInt(endPos - i);
			arr[i] = arr[randomPos];
			arr[randomPos] = tmp;
		}
	}
	
	static void shuffleArray(double[] arr, int startPos, int endPos) {
		Random rnd = new Random();
		for (int i = startPos; i < endPos; ++i) {
			double tmp = arr[i];
			int randomPos = i + rnd.nextInt(endPos - i);
			arr[i] = arr[randomPos];
			arr[randomPos] = tmp;
		}
	}
	
	private static void shuffleArray(char[] arr, int startPos, int endPos) {
		Random rnd = new Random();
		for (int i = startPos; i < endPos; ++i) {
			char tmp = arr[i];
			int randomPos = i + rnd.nextInt(endPos - i);
			arr[i] = arr[randomPos];
			arr[randomPos] = tmp;
		}
	}
	
	static boolean isPrime(int n) {
		if (n <= 1)
			return false;
		if (n <= 3)
			return true;

		if (n % 2 == 0 || n % 3 == 0)
			return false;

		for (int i = 5; i * i <= n; i = i + 6)
			if (n % i == 0 || n % (i + 2) == 0)
				return false;

		return true;
	}

	static String toString(int[] dp) {
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < dp.length; i++)
			sb.append(dp[i] + " ");
		return sb.toString();
	}
	
	static String toString(boolean[] dp) {
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < dp.length; i++)
			sb.append(dp[i] + " ");
		return sb.toString();
	}
	
	static String toString(long[] dp) {
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < dp.length; i++)
			sb.append(dp[i] + " ");
		return sb.toString();
	}
	
	static String toString(char[] dp) {
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < dp.length; i++)
			sb.append(dp[i] + "");
		return sb.toString();
	}
	
	static String toString(int[][] dp) {
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < dp.length; i++) {
			for (int j = 0; j < dp[i].length; j++) {
				sb.append(dp[i][j] + "");
			}
			sb.append('\n');
		}
		return sb.toString();
	}
	
	static String toString(long[][] dp) {
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < dp.length; i++) {
			for (int j = 0; j < dp[i].length; j++) {
				sb.append(dp[i][j] + " ");
			}
			sb.append('\n');
		}
		return sb.toString();
	}
	
	static String toString(double[][] dp) {
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < dp.length; i++) {
			for (int j = 0; j < dp[i].length; j++) {
				sb.append(dp[i][j] + " ");
			}
			sb.append('\n');
		}
		return sb.toString();
	}
	
	static String toString(char[][] dp) {
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < dp.length; i++) {
			for (int j = 0; j < dp[i].length; j++) {
				sb.append(dp[i][j] + " ");
			}
			sb.append('\n');
		}
		return sb.toString();
	}
	
	static char toChar(int i) {
		return (char) (i + 48);
	}
	
	static long mod(long a, long m) {
	    return (a%m + m) % m;
	}
	
	static long mod(long num) {
		return (num % gigamod + gigamod) % gigamod;
	}
	
	// Uses weighted quick-union with path compression.
	static class UnionFind {
	    private int[] parent;  // parent[i] = parent of i
	    private int[] size;    // size[i] = number of sites in tree rooted at i
	                           // Note: not necessarily correct if i is not a root node
	    private int count;     // number of components

	    public UnionFind(int n) {
	        count = n;
	        parent = new int[n];
	        size = new int[n];
	        for (int i = 0; i < n; i++) {
	            parent[i] = i;
	            size[i] = 1;
	        }
	    }

	    // Number of connected components.
	    public int count() {
	        return count;
	    }
	  
	    // Find the root of p.
	    public int find(int p) {
	        int root = p;
	        while (root != parent[root])
	            root = parent[root];
	        while (p != root) {
	            int newp = parent[p];
	            parent[p] = root;
	            p = newp;
	        }
	        return root;
	    }

	    public boolean connected(int p, int q) {
	        return find(p) == find(q);
	    }
	    
	    public int numConnectedTo(int node) {
	    	return size[find(node)];
	    }
	    
	    // Weighted union.
	    public void union(int p, int q) {
	        int rootP = find(p);
	        int rootQ = find(q);
	        
	        if (rootP == rootQ) return;

	        // make smaller root point to larger one
	        if (size[rootP] < size[rootQ]) {
	            parent[rootP] = rootQ;
	            size[rootQ] += size[rootP];
	        }
	        else {
	            parent[rootQ] = rootP;
	            size[rootP] += size[rootQ];
	        }
	        count--;
	    }
	    
	    public static int[] connectedComponents(UnionFind uf) {
	    	// We can do this in nlogn.
	    	
	    	int n = uf.size.length;
	    	int[] compoColors = new int[n];
	    	for (int i = 0; i < n; i++)
	    		compoColors[i] = uf.find(i);
	    	
	    	HashMap<Integer, Integer> oldToNew = new HashMap<>();
	    	int newCtr = 0;
	    	
	    	for (int i = 0; i < n; i++) {
	    		
	    		int thisOldColor = compoColors[i];
	    		Integer thisNewColor = oldToNew.get(thisOldColor);
	    		if (thisNewColor == null)
	    			thisNewColor = newCtr++;
	    		
	    		oldToNew.put(thisOldColor, thisNewColor);
	    		compoColors[i] = thisNewColor;
	    	}
	    	
	    	return compoColors;
	    }
	}
	
	static class UGraph {
		// Adjacency list.
		private TreeSet<Integer>[] adj;
		private static final String NEWLINE = "\n";
		private int E;
		
		public UGraph(int V) {
			adj = (TreeSet<Integer>[]) new TreeSet[V];
			E = 0;
			for (int i = 0; i < V; i++)
				adj[i] = new TreeSet<Integer>();
		}
		
		public void addEdge(int from, int to) {
			if (adj[from].contains(to)) return;
			E++;
			adj[from].add(to);
			adj[to].add(from);
		}
		
		public TreeSet<Integer> adj(int from) {
			return adj[from];
		}
		
		public int V() {
			return adj.length;
		}
		
		public int E() {
			return E;
		}
		
		public String toString() {
			StringBuilder s = new StringBuilder();
			s.append(V() + " vertices, " + E() + " edges " + NEWLINE);
			for (int v = 0; v < V(); v++) {
				s.append(v + ": ");
				for (int w : adj[v]) {
					s.append(w + " ");
				}
				s.append(NEWLINE);
			}
			return s.toString();
		}
		
		public static void dfsMark(int current, boolean[] marked, UGraph g) {
			if (marked[current]) return;
			
			marked[current] = true;
			Iterable<Integer> adj = g.adj(current);
			for (int adjc : adj)
				dfsMark(adjc, marked, g);
		}
		
		public static void dfsMark(int current, int from, long[] distTo, boolean[] marked, UGraph g, ArrayList<Integer> endPoints) {
			if (marked[current]) return;
			
			marked[current] = true;
			if (from != -1)
				distTo[current] = distTo[from] + 1;
			TreeSet<Integer> adj = g.adj(current);
			int alreadyMarkedCtr = 0;
			for (int adjc : adj) {
				if (marked[adjc]) alreadyMarkedCtr++;
				dfsMark(adjc, current, distTo, marked, g, endPoints);
			}
			
			if (alreadyMarkedCtr == adj.size())
				endPoints.add(current);
		}
		
		public static void bfsOrder(int current, UGraph g) {
		}
		
		public static void dfsMark(int current, int[] colorIds, int color, UGraph g) {
			if (colorIds[current] != -1) return;
			
			colorIds[current] = color;
			Iterable<Integer> adj = g.adj(current);
			for (int adjc : adj)
				dfsMark(adjc, colorIds, color, g);
		}
		
		public static int[] connectedComponents(UGraph g) {
			int n = g.V();
			int[] componentId = new int[n];
			Arrays.fill(componentId, -1);
			int colorCtr = 0;
			for (int i = 0; i < n; i++) {
				if (componentId[i] != -1) continue;
				dfsMark(i, componentId, colorCtr, g);
				colorCtr++;
			}
			
			return componentId;
		}
		
		public static boolean hasCycle(UGraph ug) {
			int n = ug.V();
			boolean[] marked = new boolean[n];
			boolean[] hasCycleFirst = new boolean[1];
			for (int i = 0; i < n; i++) {
				if (marked[i]) continue;
				hcDfsMark(i, ug, marked, hasCycleFirst, -1);
			}
			return hasCycleFirst[0];
		}
		
		// Helper for hasCycle.
		private static void hcDfsMark(int current, UGraph ug, boolean[] marked, boolean[] hasCycleFirst, int parent) {
			if (marked[current]) return;
			if (hasCycleFirst[0]) return;
			
			marked[current] = true;
			TreeSet<Integer> adjc = ug.adj(current);
			for (int adj : adjc) {
				if (marked[adj] && adj != parent && parent != -1) {
					hasCycleFirst[0] = true;
					return;
				}
				
				hcDfsMark(adj, ug, marked, hasCycleFirst, current);
			}
		}
	}
	
	static class Digraph {
		// Adjacency list.
		private HashSet<Integer>[] adj;
		private static final String NEWLINE = "\n";
		private int E;
		
		public Digraph(int V) {
			adj = (HashSet<Integer>[]) new HashSet[V];
			E = 0;
			for (int i = 0; i < V; i++)
				adj[i] = new HashSet<Integer>();
		}
		
		public void addEdge(int from, int to) {
			if (adj[from].contains(to)) return;
			E++;
			adj[from].add(to);
		}
		
		public HashSet<Integer> adj(int from) {
			return adj[from];
		}
		
		public int V() {
			return adj.length;
		}
		
		public int E() {
			return E;
		}
		
		public String toString() {
			StringBuilder s = new StringBuilder();
			s.append(V() + " vertices, " + E() + " edges " + NEWLINE);
			for (int v = 0; v < V(); v++) {
				s.append(v + ": ");
				for (int w : adj[v]) {
					s.append(w + " ");
				}
				s.append(NEWLINE);
			}
			return s.toString();
		}
		
		public static void dfsMark(int source, boolean[] marked, Digraph g) {
			if (marked[source]) return;
			
			marked[source] = true;
			Iterable<Integer> adj = g.adj(source);
			for (int adjc : adj)
				dfsMark(adjc, marked, g);
		}
		
		public static void bfsOrder(int source, Digraph g) {
		}
		
		private static void dfsMark(int source, int[] colorIds, int color, Digraph g) {
			if (colorIds[source] != -1) return;
			
			colorIds[source] = color;
			Iterable<Integer> adj = g.adj(source);
			for (int adjc : adj)
				dfsMark(adjc, colorIds, color, g);
		}
		
		public static int[] connectedComponents(Digraph g) {
			int n = g.V();
			int[] componentId = new int[n];
			Arrays.fill(componentId, -1);
			int colorCtr = 0;
			for (int i = 0; i < n; i++) {
				if (componentId[i] != -1) continue;
				dfsMark(i, componentId, colorCtr, g);
				colorCtr++;
			}
			
			return componentId;
		}
		
		public static Stack<Integer> topologicalSort(Digraph dg)
		{
			// dg has to be a directed acyclic graph.
			// We'll have to run dfs on the digraph and push the deepest nodes on stack first.
			// We'll need a Stack<Integer> and a int[] marked.
			Stack<Integer> topologicalStack = new Stack<Integer>();
			boolean[] marked = new boolean[dg.V()];
			
			// Calling dfs
			for (int i = 0; i < dg.V(); i++)
			{
				if (!marked[i]) runDfs(dg, topologicalStack, marked, i);
			}
			
			return topologicalStack;
		}
		
		static void runDfs(Digraph dg, Stack<Integer> topologicalStack, boolean[] marked, int source)
		{
			marked[source] = true;
			for (Integer adjVertex : dg.adj(source))
			{
				if (!marked[adjVertex]) runDfs(dg, topologicalStack, marked, adjVertex);
			}
			topologicalStack.add(source);
		}
	}
	
	static class FastReader {
		private BufferedReader bfr;
		private StringTokenizer st;

		public FastReader() {
			bfr = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			if (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(bfr.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		char nextChar() {
			return next().toCharArray()[0];
		}

		String nextString() {
			return next();
		}

		int[] nextIntArray(int n) {
			int[] arr = new int[n];
			for (int i = 0; i < n; i++)
				arr[i] = nextInt();
			return arr;
		}
		
		int[] nextOneIntArray(int n) {
			int[] arr = new int[n + 1];
			for (int i = 1; i < n; i++)
				arr[i] = nextInt();
			return arr;
		}

		double[] nextDoubleArray(int n) {
			double[] arr = new double[n];
			for (int i = 0; i < arr.length; i++)
				arr[i] = nextDouble();
			return arr;
		}

		long[] nextLongArray(int n) {
			long[] arr = new long[n];
			for (int i = 0; i < n; i++)
				arr[i] = nextLong();
			return arr;
		}
		
		/*public char[] nextCharArray(int n) {
			char[] chars = new char[n];
			for (int i = 0; i < n; i++)
				chars[i] = fr.nextChar();
			return chars;
		}*/
	}
	
	private static class IndexMaxPQ<Key extends Comparable<Key>> implements Iterable<Integer> {
	    private int maxN;        // maximum number of elements on PQ
	    private int n;           // number of elements on PQ
	    private int[] pq;        // binary heap using 1-based indexing
	    private int[] qp;        // inverse of pq - qp[pq[i]] = pq[qp[i]] = i
	    private Key[] keys;      // keys[i] = priority of i

	    /**
	     * Initializes an empty indexed priority queue with indices between {@code 0}
	     * and {@code maxN - 1}.
	     *
	     * @param  maxN the keys on this priority queue are index from {@code 0} to {@code maxN - 1}
	     * @throws IllegalArgumentException if {@code maxN < 0}
	     */
	    public IndexMaxPQ(int maxN) {
	        if (maxN < 0) throw new IllegalArgumentException();
	        this.maxN = maxN;
	        n = 0;
	        keys = (Key[]) new Comparable[maxN + 1];    // make this of length maxN??
	        pq   = new int[maxN + 1];
	        qp   = new int[maxN + 1];                   // make this of length maxN??
	        for (int i = 0; i <= maxN; i++)
	            qp[i] = -1;
	    }

	    /**
	     * Returns true if this priority queue is empty.
	     *
	     * @return {@code true} if this priority queue is empty;
	     *         {@code false} otherwise
	     */
	    public boolean isEmpty() {
	        return n == 0;
	    }

	    /**
	     * Is {@code i} an index on this priority queue?
	     *
	     * @param  i an index
	     * @return {@code true} if {@code i} is an index on this priority queue;
	     *         {@code false} otherwise
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     */
	    public boolean contains(int i) {
	        validateIndex(i);
	        return qp[i] != -1;
	    }

	    /**
	     * Returns the number of keys on this priority queue.
	     *
	     * @return the number of keys on this priority queue 
	     */
	    public int size() {
	        return n;
	    }

	   /**
	     * Associate key with index i.
	     *
	     * @param  i an index
	     * @param  key the key to associate with index {@code i}
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @throws IllegalArgumentException if there already is an item
	     *         associated with index {@code i}
	     */
	    public void insert(int i, Key key) {
	        validateIndex(i);
	        if (contains(i)) throw new IllegalArgumentException("index is already in the priority queue");
	        n++;
	        qp[i] = n;
	        pq[n] = i;
	        keys[i] = key;
	        swim(n);
	    }

	    /**
	     * Returns an index associated with a maximum key.
	     *
	     * @return an index associated with a maximum key
	     * @throws NoSuchElementException if this priority queue is empty
	     */
	    public int maxIndex() {
	        if (n == 0) throw new NoSuchElementException("Priority queue underflow");
	        return pq[1];
	    }

	    /**
	     * Returns a maximum key.
	     *
	     * @return a maximum key
	     * @throws NoSuchElementException if this priority queue is empty
	     */
	    public Key maxKey() {
	        if (n == 0) throw new NoSuchElementException("Priority queue underflow");
	        return keys[pq[1]];
	    }

	    /**
	     * Removes a maximum key and returns its associated index.
	     *
	     * @return an index associated with a maximum key
	     * @throws NoSuchElementException if this priority queue is empty
	     */
	    public int delMax() {
	        if (n == 0) throw new NoSuchElementException("Priority queue underflow");
	        int max = pq[1];
	        exch(1, n--);
	        sink(1);

	        assert pq[n+1] == max;
	        qp[max] = -1;        // delete
	        keys[max] = null;    // to help with garbage collection
	        pq[n+1] = -1;        // not needed
	        return max;
	    }

	    /**
	     * Returns the key associated with index {@code i}.
	     *
	     * @param  i the index of the key to return
	     * @return the key associated with index {@code i}
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @throws NoSuchElementException no key is associated with index {@code i}
	     */
	    public Key keyOf(int i) {
	        validateIndex(i);
	        if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
	        else return keys[i];
	    }

	    /**
	     * Change the key associated with index {@code i} to the specified value.
	     *
	     * @param  i the index of the key to change
	     * @param  key change the key associated with index {@code i} to this key
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     */
	    public void changeKey(int i, Key key) {
	        validateIndex(i);
	        if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
	        keys[i] = key;
	        swim(qp[i]);
	        sink(qp[i]);
	    }

	   /**
	     * Change the key associated with index {@code i} to the specified value.
	     *
	     * @param  i the index of the key to change
	     * @param  key change the key associated with index {@code i} to this key
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @deprecated Replaced by {@code changeKey(int, Key)}.
	     */
	    @Deprecated
	    public void change(int i, Key key) {
	        validateIndex(i);
	        changeKey(i, key);
	    }

	    /**
	     * Increase the key associated with index {@code i} to the specified value.
	     *
	     * @param  i the index of the key to increase
	     * @param  key increase the key associated with index {@code i} to this key
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @throws IllegalArgumentException if {@code key <= keyOf(i)}
	     * @throws NoSuchElementException no key is associated with index {@code i}
	     */
	    public void increaseKey(int i, Key key) {
	        validateIndex(i);
	        if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
	        if (keys[i].compareTo(key) == 0)
	            throw new IllegalArgumentException("Calling increaseKey() with a key equal to the key in the priority queue");
	        if (keys[i].compareTo(key) > 0)
	            throw new IllegalArgumentException("Calling increaseKey() with a key that is strictly less than the key in the priority queue");

	        keys[i] = key;
	        swim(qp[i]);
	    }

	    /**
	     * Decrease the key associated with index {@code i} to the specified value.
	     *
	     * @param  i the index of the key to decrease
	     * @param  key decrease the key associated with index {@code i} to this key
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @throws IllegalArgumentException if {@code key >= keyOf(i)}
	     * @throws NoSuchElementException no key is associated with index {@code i}
	     */
	    public void decreaseKey(int i, Key key) {
	        validateIndex(i);
	        if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
	        if (keys[i].compareTo(key) == 0)
	            throw new IllegalArgumentException("Calling decreaseKey() with a key equal to the key in the priority queue");
	        if (keys[i].compareTo(key) < 0)
	            throw new IllegalArgumentException("Calling decreaseKey() with a key that is strictly greater than the key in the priority queue");
	        keys[i] = key;
	        sink(qp[i]);
	    }

	    /**
	     * Remove the key on the priority queue associated with index {@code i}.
	     *
	     * @param  i the index of the key to remove
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @throws NoSuchElementException no key is associated with index {@code i}
	     */
	    public void delete(int i) {
	        validateIndex(i);
	        if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
	        int index = qp[i];
	        exch(index, n--);
	        swim(index);
	        sink(index);
	        keys[i] = null;
	        qp[i] = -1;
	    }

	    // throw an IllegalArgumentException if i is an invalid index
	    private void validateIndex(int i) {
	        if (i < 0) throw new IllegalArgumentException("index is negative: " + i);
	        if (i >= maxN) throw new IllegalArgumentException("index >= capacity: " + i);
	    }

	   /***************************************************************************
	    * General helper functions.
	    ***************************************************************************/
	    private boolean less(int i, int j) {
	        return keys[pq[i]].compareTo(keys[pq[j]]) < 0;
	    }

	    private void exch(int i, int j) {
	        int swap = pq[i];
	        pq[i] = pq[j];
	        pq[j] = swap;
	        qp[pq[i]] = i;
	        qp[pq[j]] = j;
	    }


	   /***************************************************************************
	    * Heap helper functions.
	    ***************************************************************************/
	    private void swim(int k) {
	        while (k > 1 && less(k/2, k)) {
	            exch(k, k/2);
	            k = k/2;
	        }
	    }

	    private void sink(int k) {
	        while (2*k <= n) {
	            int j = 2*k;
	            if (j < n && less(j, j+1)) j++;
	            if (!less(k, j)) break;
	            exch(k, j);
	            k = j;
	        }
	    }


	    /**
	     * Returns an iterator that iterates over the keys on the
	     * priority queue in descending order.
	     * The iterator doesn't implement {@code remove()} since it's optional.
	     *
	     * @return an iterator that iterates over the keys in descending order
	     */
	    public Iterator<Integer> iterator() {
	        return new HeapIterator();
	    }

	    private class HeapIterator implements Iterator<Integer> {
	        // create a new pq
	        private IndexMaxPQ<Key> copy;

	        // add all elements to copy of heap
	        // takes linear time since already in heap order so no keys move
	        public HeapIterator() {
	            copy = new IndexMaxPQ<Key>(pq.length - 1);
	            for (int i = 1; i <= n; i++)
	                copy.insert(pq[i], keys[pq[i]]);
	        }

	        public boolean hasNext()  { return !copy.isEmpty();                     }
	        public void remove()      { throw new UnsupportedOperationException();  }

	        public Integer next() {
	            if (!hasNext()) throw new NoSuchElementException();
	            return copy.delMax();
	        }
	    }

	    /*public static void main(String[] args) {
	        // insert a bunch of strings
	        String[] strings = { "it", "was", "the", "best", "of", "times", "it", "was", "the", "worst" };

	        IndexMaxPQ<String> pq = new IndexMaxPQ<String>(strings.length);
	        for (int i = 0; i < strings.length; i++) {
	            pq.insert(i, strings[i]);
	        }

	        // print each key using the iterator
	        for (int i : pq) {
	            StdOut.println(i + " " + strings[i]);
	        }

	        StdOut.println();

	        // increase or decrease the key
	        for (int i = 0; i < strings.length; i++) {
	            if (StdRandom.uniform() < 0.5)
	                pq.increaseKey(i, strings[i] + strings[i]);
	            else
	                pq.decreaseKey(i, strings[i].substring(0, 1));
	        }

	        // delete and print each key
	        while (!pq.isEmpty()) {
	            String key = pq.maxKey();
	            int i = pq.delMax();
	            StdOut.println(i + " " + key);
	        }
	        StdOut.println();

	        // reinsert the same strings
	        for (int i = 0; i < strings.length; i++) {
	            pq.insert(i, strings[i]);
	        }

	        // delete them in random order
	        int[] perm = new int[strings.length];
	        for (int i = 0; i < strings.length; i++)
	            perm[i] = i;
	        StdRandom.shuffle(perm);
	        for (int i = 0; i < perm.length; i++) {
	            String key = pq.keyOf(perm[i]);
	            pq.delete(perm[i]);
	            StdOut.println(perm[i] + " " + key);
	        }

	    }*/
	}
	
	public static class IndexMinPQ<Key extends Comparable<Key>> implements Iterable<Integer> {
	    private int maxN;        // maximum number of elements on PQ
	    private int n;           // number of elements on PQ
	    private int[] pq;        // binary heap using 1-based indexing
	    private int[] qp;        // inverse of pq - qp[pq[i]] = pq[qp[i]] = i
	    private Key[] keys;      // keys[i] = priority of i

	    /**
	     * Initializes an empty indexed priority queue with indices between {@code 0}
	     * and {@code maxN - 1}.
	     * @param  maxN the keys on this priority queue are index from {@code 0}
	     *         {@code maxN - 1}
	     * @throws IllegalArgumentException if {@code maxN < 0}
	     */
	    public IndexMinPQ(int maxN) {
	        if (maxN < 0) throw new IllegalArgumentException();
	        this.maxN = maxN;
	        n = 0;
	        keys = (Key[]) new Comparable[maxN + 1];    // make this of length maxN??
	        pq   = new int[maxN + 1];
	        qp   = new int[maxN + 1];                   // make this of length maxN??
	        for (int i = 0; i <= maxN; i++)
	            qp[i] = -1;
	    }

	    /**
	     * Returns true if this priority queue is empty.
	     *
	     * @return {@code true} if this priority queue is empty;
	     *         {@code false} otherwise
	     */
	    public boolean isEmpty() {
	        return n == 0;
	    }

	    /**
	     * Is {@code i} an index on this priority queue?
	     *
	     * @param  i an index
	     * @return {@code true} if {@code i} is an index on this priority queue;
	     *         {@code false} otherwise
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     */
	    public boolean contains(int i) {
	        validateIndex(i);
	        return qp[i] != -1;
	    }

	    /**
	     * Returns the number of keys on this priority queue.
	     *
	     * @return the number of keys on this priority queue
	     */
	    public int size() {
	        return n;
	    }

	    /**
	     * Associates key with index {@code i}.
	     *
	     * @param  i an index
	     * @param  key the key to associate with index {@code i}
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @throws IllegalArgumentException if there already is an item associated
	     *         with index {@code i}
	     */
	    public void insert(int i, Key key) {
	        validateIndex(i);
	        if (contains(i)) throw new IllegalArgumentException("index is already in the priority queue");
	        n++;
	        qp[i] = n;
	        pq[n] = i;
	        keys[i] = key;
	        swim(n);
	    }

	    /**
	     * Returns an index associated with a minimum key.
	     *
	     * @return an index associated with a minimum key
	     * @throws NoSuchElementException if this priority queue is empty
	     */
	    public int minIndex() {
	        if (n == 0) throw new NoSuchElementException("Priority queue underflow");
	        return pq[1];
	    }

	    /**
	     * Returns a minimum key.
	     *
	     * @return a minimum key
	     * @throws NoSuchElementException if this priority queue is empty
	     */
	    public Key minKey() {
	        if (n == 0) throw new NoSuchElementException("Priority queue underflow");
	        return keys[pq[1]];
	    }

	    /**
	     * Removes a minimum key and returns its associated index.
	     * @return an index associated with a minimum key
	     * @throws NoSuchElementException if this priority queue is empty
	     */
	    public int delMin() {
	        if (n == 0) throw new NoSuchElementException("Priority queue underflow");
	        int min = pq[1];
	        exch(1, n--);
	        sink(1);
	        assert min == pq[n+1];
	        qp[min] = -1;        // delete
	        keys[min] = null;    // to help with garbage collection
	        pq[n+1] = -1;        // not needed
	        return min;
	    }

	    /**
	     * Returns the key associated with index {@code i}.
	     *
	     * @param  i the index of the key to return
	     * @return the key associated with index {@code i}
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @throws NoSuchElementException no key is associated with index {@code i}
	     */
	    public Key keyOf(int i) {
	        validateIndex(i);
	        if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
	        else return keys[i];
	    }

	    /**
	     * Change the key associated with index {@code i} to the specified value.
	     *
	     * @param  i the index of the key to change
	     * @param  key change the key associated with index {@code i} to this key
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @throws NoSuchElementException no key is associated with index {@code i}
	     */
	    public void changeKey(int i, Key key) {
	        validateIndex(i);
	        if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
	        keys[i] = key;
	        swim(qp[i]);
	        sink(qp[i]);
	    }

	    /**
	     * Change the key associated with index {@code i} to the specified value.
	     *
	     * @param  i the index of the key to change
	     * @param  key change the key associated with index {@code i} to this key
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @deprecated Replaced by {@code changeKey(int, Key)}.
	     */
	    @Deprecated
	    public void change(int i, Key key) {
	        changeKey(i, key);
	    }

	    /**
	     * Decrease the key associated with index {@code i} to the specified value.
	     *
	     * @param  i the index of the key to decrease
	     * @param  key decrease the key associated with index {@code i} to this key
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @throws IllegalArgumentException if {@code key >= keyOf(i)}
	     * @throws NoSuchElementException no key is associated with index {@code i}
	     */
	    public void decreaseKey(int i, Key key) {
	        validateIndex(i);
	        if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
	        if (keys[i].compareTo(key) == 0)
	            throw new IllegalArgumentException("Calling decreaseKey() with a key equal to the key in the priority queue");
	        if (keys[i].compareTo(key) < 0)
	            throw new IllegalArgumentException("Calling decreaseKey() with a key strictly greater than the key in the priority queue");
	        keys[i] = key;
	        swim(qp[i]);
	    }

	    /**
	     * Increase the key associated with index {@code i} to the specified value.
	     *
	     * @param  i the index of the key to increase
	     * @param  key increase the key associated with index {@code i} to this key
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @throws IllegalArgumentException if {@code key <= keyOf(i)}
	     * @throws NoSuchElementException no key is associated with index {@code i}
	     */
	    public void increaseKey(int i, Key key) {
	        validateIndex(i);
	        if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
	        if (keys[i].compareTo(key) == 0)
	            throw new IllegalArgumentException("Calling increaseKey() with a key equal to the key in the priority queue");
	        if (keys[i].compareTo(key) > 0)
	            throw new IllegalArgumentException("Calling increaseKey() with a key strictly less than the key in the priority queue");
	        keys[i] = key;
	        sink(qp[i]);
	    }

	    /**
	     * Remove the key associated with index {@code i}.
	     *
	     * @param  i the index of the key to remove
	     * @throws IllegalArgumentException unless {@code 0 <= i < maxN}
	     * @throws NoSuchElementException no key is associated with index {@code i}
	     */
	    public void delete(int i) {
	        validateIndex(i);
	        if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
	        int index = qp[i];
	        exch(index, n--);
	        swim(index);
	        sink(index);
	        keys[i] = null;
	        qp[i] = -1;
	    }

	    // throw an IllegalArgumentException if i is an invalid index
	    private void validateIndex(int i) {
	        if (i < 0) throw new IllegalArgumentException("index is negative: " + i);
	        if (i >= maxN) throw new IllegalArgumentException("index >= capacity: " + i);
	    }

	   /***************************************************************************
	    * General helper functions.
	    ***************************************************************************/
	    private boolean greater(int i, int j) {
	        return keys[pq[i]].compareTo(keys[pq[j]]) > 0;
	    }

	    private void exch(int i, int j) {
	        int swap = pq[i];
	        pq[i] = pq[j];
	        pq[j] = swap;
	        qp[pq[i]] = i;
	        qp[pq[j]] = j;
	    }


	   /***************************************************************************
	    * Heap helper functions.
	    ***************************************************************************/
	    private void swim(int k) {
	        while (k > 1 && greater(k/2, k)) {
	            exch(k, k/2);
	            k = k/2;
	        }
	    }

	    private void sink(int k) {
	        while (2*k <= n) {
	            int j = 2*k;
	            if (j < n && greater(j, j+1)) j++;
	            if (!greater(k, j)) break;
	            exch(k, j);
	            k = j;
	        }
	    }


	   /***************************************************************************
	    * Iterators.
	    ***************************************************************************/

	    /**
	     * Returns an iterator that iterates over the keys on the
	     * priority queue in ascending order.
	     * The iterator doesn't implement {@code remove()} since it's optional.
	     *
	     * @return an iterator that iterates over the keys in ascending order
	     */
	    public Iterator<Integer> iterator() { return new HeapIterator(); }

	    private class HeapIterator implements Iterator<Integer> {
	        // create a new pq
	        private IndexMinPQ<Key> copy;

	        // add all elements to copy of heap
	        // takes linear time since already in heap order so no keys move
	        public HeapIterator() {
	            copy = new IndexMinPQ<Key>(pq.length - 1);
	            for (int i = 1; i <= n; i++)
	                copy.insert(pq[i], keys[pq[i]]);
	        }

	        public boolean hasNext()  { return !copy.isEmpty();                     }
	        public void remove()      { throw new UnsupportedOperationException();  }

	        public Integer next() {
	            if (!hasNext()) throw new NoSuchElementException();
	            return copy.delMin();
	        }
	    }


	    /**
	     * Unit tests the {@code IndexMinPQ} data type.
	     *
	     * @param args the command-line arguments
	     */
	   /* public static void main(String[] args) {
	        // insert a bunch of strings
	        String[] strings = { "it", "was", "the", "best", "of", "times", "it", "was", "the", "worst" };

	        IndexMinPQ<String> pq = new IndexMinPQ<String>(strings.length);
	        for (int i = 0; i < strings.length; i++) {
	            pq.insert(i, strings[i]);
	        }

	        // delete and print each key
	        while (!pq.isEmpty()) {
	            int i = pq.delMin();
	            StdOut.println(i + " " + strings[i]);
	        }
	        StdOut.println();

	        // reinsert the same strings
	        for (int i = 0; i < strings.length; i++) {
	            pq.insert(i, strings[i]);
	        }

	        // print each key using the iterator
	        for (int i : pq) {
	            StdOut.println(i + " " + strings[i]);
	        }
	        while (!pq.isEmpty()) {
	            pq.delMin();
	        }

	    }*/
	}
}

// NOTES: 
// ASCII VALUE OF 'A': 65
// ASCII VALUE OF 'a': 97
// Range of long: 9 * 10^18
// ASCII VALUE OF '0': 48