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.InputStream;
import java.io.InputStreamReader;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Random;
import java.util.Scanner;
import java.util.Stack;
import java.util.StringTokenizer;


public class R290 {
	public static void main(String[] args) {
		foxAndNames2(System.in);
	}		
	
	public static void foxAndNames2(InputStream in) {
		MyScanner scan = new MyScanner(in);
		int n = scan.nextInt();
		char[][] a = new char[n][];
		String[] s = new String[n];
		for (int i = 0; i < a.length; i++) {
			s[i] = scan.nextLine();
			a[i] = s[i].toCharArray();
		}
		HashMap<Integer, ArrayList<Integer>> dep = new HashMap<>();
		for (int i = 0; i < 26; i++) {
			dep.put(i, new ArrayList<Integer>());
		}
		for (int i = 1; i < a.length; i++) {
			if (s[i].indexOf(s[i-1]) == 0) {
				continue;
			} else if (s[i-1].indexOf(s[i]) == 0) {
				System.out.println("Impossible");
				return;
			} else {
				int t = 0;
				while (t < a[i].length && t < a[i-1].length && a[i][t] == a[i-1][t]) {
					t++;
				}
				if (t < a[i].length && t < a[i-1].length) {
					if (!dep.get(a[i-1][t] - 'a').contains(a[i][t] - 'a')) {
						dep.get(a[i-1][t] - 'a').add(a[i][t] - 'a');
					}
				}
			}
		}
		
		ArrayList<Integer> order = new ArrayList<>();
		if (!topSortIter(order, dep)) {
			System.out.println("Impossible");
			return;
		}
		
		String ret = "";
		for (int i = 0; i < order.size(); i++) {
			ret += (char)(order.get(i) +  'a');
		}
		System.out.println(ret);
	}
	
	@SuppressWarnings("unchecked")
	public static boolean topSortIter(ArrayList<Integer> order, HashMap<Integer, ArrayList<Integer>> graphRef) {
		
		// Create a copy of the graph
		HashMap<Integer, ArrayList<Integer>> graph = new HashMap<>();
		for (Integer key: graphRef.keySet()) {
			graph.put(key, (ArrayList<Integer>) graphRef.get(key).clone());
		}
		
		// Count number of incoming edges
		HashMap<Integer, Integer> numIncoming = new HashMap<>();
		for (Integer key: graph.keySet()) {
			ArrayList<Integer> children = graph.get(key);
			for (Integer child: children) {
				numIncoming.put(child, numIncoming.containsKey(child) ? numIncoming.get(child) + 1 : 1);
			}
		}
		
		// Select vertices with no incoming edges
		Stack<Integer> roots = new Stack<>(); // Doesn't have to be a stack!
		for (Integer key: graph.keySet()) {
			if (!numIncoming.containsKey(key) || numIncoming.get(key) == 0) {
				roots.push(key);
			}
		}
		
		// Build the ordering
		while (!roots.isEmpty()) {
			Integer top = roots.pop();
			order.add(top);
			ArrayList<Integer> children = graph.get(top);
			for (int i = 0; i < children.size(); i++) {
				Integer rem = children.remove(i--);
				numIncoming.put(rem, numIncoming.get(rem) - 1);
				if (numIncoming.get(rem) == 0) {
					roots.push(rem);
				}
			}
		}
		
		// Count number of edges
		int edges = 0;
		for (Integer key: graph.keySet()) {
			edges += graph.get(key).size();
		}
		
		return edges > 0 ? false : true;
	}
	
//	public static boolean topSortIter(ArrayList<Character> order, HashMap<Character, HashSet<Character>> dep) {
//		HashSet<Character> visited = new HashSet<>();
//		HashSet<Character> workingSet = new HashSet<>();
//		Stack<Character> stack = new Stack<>();
//		for (char i: dep.keySet()) {
//			if (!visited.contains(i)) {
//				char c = i;
//				stack.add(c);
//				while (!stack.isEmpty()) {
//					c = stack.pop();
//					if (workingSet.contains(c)) {
//						// Cycle detected!
//						return false;
//					}
//					if (!visited.contains(c)) {
//						workingSet.add(c);
//						HashSet<Character> children = dep.get(c);
//						for (char child: children) {
//							stack.add(child);
//						}
//						visited.add(c);
//						workingSet.remove(c);
//						order.add(c);
//					}
//				}
//			}
//		}
//		Collections.reverse(order);
//		return true;
//	}
	
	public static boolean topSortRecur(ArrayList<Character> order, HashMap<Character, HashSet<Character>> dep) {

		HashSet<Character> visited = new HashSet<>();
		HashSet<Character> workingSet = new HashSet<>();
		
		for (char c: dep.keySet()) {
			if (!visited.contains(c)) {
				if (!visit(c, visited, workingSet, order, dep)) {
					return false;
				}
			}
		}
		Collections.reverse(order);
		return true;
	}
	
	public static boolean visit(char c, HashSet<Character> visited, HashSet<Character> workingSet, ArrayList<Character> order, HashMap<Character, HashSet<Character>> dep) {
		if (workingSet.contains(c)) {
			return false;
		}
		if (!visited.contains(c)) {
			workingSet.add(c);
			HashSet<Character> children = dep.get(c);
			for (char child: children) {
				if (!visit(child, visited, workingSet, order, dep)) {
					return false;
				}
			}
			visited.add(c);
			workingSet.remove(c);
			order.add(c);
		}
		return true;
	}

	public static void foxAndNames(InputStream in) {
		MyScanner scan = new MyScanner(in);
		int n = scan.nextInt();
		char[][] a = new char[n][];
		String[] s = new String[n];
		for (int i = 0; i < a.length; i++) {
			s[i] = scan.nextLine();
			a[i] = s[i].toCharArray();
		}
		HashMap<Character, HashSet<Character>> dep = new HashMap<>();
		for (int i = 0; i < 26; i++) {
			dep.put((char) (i + 'a'), new HashSet<Character>());
		}
		for (int i = 1; i < a.length; i++) {
			if (s[i].indexOf(s[i-1]) == 0) {
				continue;
			} else if (s[i-1].indexOf(s[i]) == 0) {
				System.out.println("Impossible");
				return;
			} else {
				int t = 0;
				while (t < a[i].length && t < a[i-1].length && a[i][t] == a[i-1][t]) {
					t++;
				}
				if (t < a[i].length && t < a[i-1].length) {
					dep.get(a[i-1][t]).add(a[i][t]);
				}
			}
		}
		
		int maxDepth = 1;
		int maxIdx = 0;
		ArrayList<int[]> depths = new ArrayList<>();
		for (int c = 0; c < 26; c++) {
			char top = (char) (c + 'a');
			char start = top;
			Stack<Character> st = new Stack<Character>();
			HashSet<Character> visited = new HashSet<>();
			st.add(top);
			boolean valid = true;
			int depth = 0;
			boolean first = true;
			while (!st.isEmpty()) {
				top = st.pop();
				if (!first && top == start) {
					valid = false; // Loop!
					break;
				}
				first = false;
				if (visited.contains(top)) {
					continue;
				}
				depth++;
				visited.add(top);
				if (dep.containsKey(top)) {
					HashSet<Character> children = dep.get(top);
					for (char child: children) {
						st.push(child);
					}
				}
			}
			
			if (!valid) {
				System.out.println("Impossible");
				return;
			}
			//if (depth > maxDepth) {
				depths.add(new int[]{depth , c});
				maxDepth = depth;
				maxIdx = c;
			//}
		}
		Collections.sort(depths, new Comparator<int[]>(){
			@Override
			public int compare(int[] o1, int[] o2) {
				return Integer.compare(o2[0], o1[0]);
			}			
		});
		
//		Queue<Character> st = new LinkedList<Character>();
//		char top = (char)(maxIdx + 'a');
//		st.add(top);
//		while (!st.isEmpty()) {
//			top = st.poll();
//			visited.add(top);
//			order.add(top);
//			if (dep.containsKey(top)) {
//				HashSet<Character> children = dep.get(top);
//				for (char child: children) {
//					st.add(child);
//				}
//			}
//		}
		
		int[] depth = new int[26];
		Arrays.fill(depth, -1);
		maxDepth = 0;
		for (int i = 0; i < depths.size(); i++) {
			char top = (char) (depths.get(i)[1] + 'a');
			char start = top;
			depth[depths.get(i)[1]] = depth(top, dep, depth);
			maxDepth = Math.max(maxDepth, depth[depths.get(i)[1]]);
		}
		
		ArrayList<Character> order = new ArrayList<>();
		for (int i = maxDepth; i >= -1; i--) {
			for (int j = 0; j < depth.length; j++) {
				if (depth[j] == i) {
					order.add((char) (j + 'a'));
				}
			}
		}
		
		//HashSet<Character> visited = new HashSet<>();
		
//		char[] alpha = "abcdefghijklmnopqrstuvwxyz".toCharArray();
//		for (int i = 0; i < alpha.length; i++) {
//			//if (!visited.contains(alpha[i])) {
//			order.add(alpha[i]);
//			//}
//		}
//		
//		for (int i = 0; i < alpha.length; i++) {
//			int bestIdx = alpha.length-1;
//			char top = (char)(i + 'a');
//			HashSet<Character> after = (HashSet<Character>) dep.get(top).clone();
//			for (int j = 0; j < alpha.length; j++) {
//				if (after.contains(order.get(j))) {
//					
//				}
//				if (after.isEmpty()) {
//					break;
//				}
//			} 
//		}
		String ret = "";
		for (int i = 0; i < order.size(); i++) {
			ret += order.get(i);
		}
		System.out.println(ret);
	}

	public static int depth(char top, HashMap<Character, HashSet<Character>> dep, int[] depth) {
		if (depth[top - 'a'] > -1) {
			return depth[top - 'a'];
		}
		int max = 0;
		HashSet<Character> children = dep.get(top);
		for (char child: children) {
			max = Math.max(max, depth(child, dep, depth) + 1);
		}
		depth[top - 'a'] = max;
		return max;
	}

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner(InputStream in) {
			this.br = new BufferedReader(new InputStreamReader(in));
		}

		public void close() {
			try {
				this.br.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}

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

		long[] nextLongArray(int n) {
			long[] a = new long[n];
			for (int i = 0; i < a.length; i++) {
				a[i] = this.nextLong();
			}
			return a;
		}

		int[] nextIntArray(int n) {
			int[] a = new int[n];
			for (int i = 0; i < a.length; i++) {
				a[i] = this.nextInt();
			}
			return a;
		}

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

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

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

		String nextLine(){
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}
	}
}