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.*;
import java.lang.reflect.Array;
import java.math.BigInteger;
import java.util.*;

/**
 *
 * @author Saju
 *
 */

public class Main {

	static int[] dx = { 0, 1, 0, -1 };
	static int[] dy = { -1, 0, 1, 0 };

	static int[] ddx = { 0, 1, 0, -1, -1, 1, 1, -1 };
	static int[] ddy = { -1, 0, 1, 0, -1, -1, 1, 1 };

	static int[] kx = { 2, 1, -1, -2, -2, -1, 1, 2 };
	static int[] ky = { 1, 2, 2, 1, -1, -2, -2, -1 };

	static long MOD = Long.MAX_VALUE;

	static final int MAX = 100007;
	static long INF = Long.MAX_VALUE;

	static double PI = 3.1415926535;

	private static final double EPSILON = 1e-10;

	private static double dp[] = new double[MAX];

	public static void main(String[] args) {

		InputReader in = new InputReader(System.in);

		/*

4 5
1 2
2 3
3 4
5 2 3 8
+ 2 5

5 8
4 3
3 1
5 2
1 2
1 10 4 9 4
+ 1 6
? 3
+ 3 5
? 3
+ 2 2
+ 5 10
? 5
? 4

		 */
		
		
		
		int n = in.nextInt();
		String str = in.next();
		
		List<Integer> adjList[] = new ArrayList[26];
		for(int i = 0; i < 26; i++){
			adjList[i] = new ArrayList<Integer>();
		}
		for(int i = 0; i < n - 1; i++){
			String str1 = in.next();
			
			for(int j = 0; j < str.length() && j < str1.length(); j++){
				if(str.charAt(j) != str1.charAt(j)){
					int u = str.charAt(j) - 97;
					int v = str1.charAt(j) - 97;
					adjList[u].add(v);
					break;
				}
				if(j == str1.length() - 1 && str1.length() < str.length()){
					System.out.println("Impossible");
					return;
				}
			}
			
			str = new String(str1);
		}
		
		detectCycle(adjList);
		
		if(hasCycle){
			System.out.println("Impossible");
		}
		else{
			topologicalSort(adjList);
		}
		
		System.exit(0);
	}

	

	private static void topologicalSort(List<Integer>[] adjList) {
		boolean[] visited = new boolean[26];
		
		
		for(int i = 0; i < 26; i++){
			if(!visited[i]){
				dfs(i, adjList, visited);
			}
		}
		Iterator<Character> chit = deque.iterator();
		while(chit.hasNext()){
			System.out.print(chit.next());
		}
		System.out.println();
	}
	static String str = "";
	static Deque<Character> deque = new LinkedList<Character>();
	private static void dfs(int u, List<Integer>[] adjList, boolean[] visited) {
		visited[u] = true;
		for(int v : adjList[u]){
			if(!visited[v]){
				dfs(v, adjList, visited);
			}
		}
		char ch = (char) (97 + u);
//		str = String.valueOf(ch) + str;
//		System.out.println(str);
		deque.addFirst(ch);
	}

	private static boolean hasCycle = false;
	private static void detectCycle(List<Integer>[] adjList) {
		boolean [] visited = new boolean[26];
		boolean[] onPath = new boolean[26];
		
		for(int i = 0; i < 26; i++){
			if(!visited[i] && !hasCycle){
				dfs(i, adjList, visited, onPath);
			}
		}
	}



	private static void dfs(int u, List<Integer>[] adjList, boolean[] visited, boolean[] onPath) {
		if(hasCycle){
			return;
		}
		
		visited[u] = true;
		onPath[u] = true;
		
		for(int v : adjList[u]){
			if(!visited[v]){
				dfs(v, adjList, visited, onPath);
			}
			else if(onPath[v]){
				hasCycle = true;
				return;
			}
		}
		onPath[u] = false;
	}



	private static class Node{
		long value;
		List<Integer> childs;
		
		Node(long value){
			this.value = value;
			childs = new ArrayList<Integer>();
		}
	}
	

	private static class Pair {
		int first;
		String second;

		Pair(int first, String second) {
			this.first = first;
			this.second = second;
		}
	}

	private static class Point {
		int x;
		int y;

		Point(int x, int y) {
			this.x = x;
			this.y = y;
		}

		@Override
		public String toString() {

			return this.x + " " + this.y;
		}
	}

	// private static long set(long N, int pos) {
	//
	// return N = N | (1 << pos);
	// }
	// private static long check(long N, int pos) {
	//
	// return N & (1 << pos);
	// }
	// private static long reset(long N, int pos){
	//
	// return N=N|~(1<<pos);
	// }

	// nCk
	// private static long binomialCoeff(int n, int k){
	// long[] arr = new long[k + 1];
	// arr[0] = 1;
	// for(int i = 1; i <= n; i++){
	// for(int j = Math.min(i, k); j > 0; j--){
	// arr[j] = (arr[j] + arr[j - 1]) % MOD;
	// }
	// }
	// return arr[k];
	// }

	// BIT =>
	// https://www.hackerearth.com/practice/notes/binary-indexed-tree-or-fenwick-tree/
	// static int BIT[] = new int[MAX + 5];
	//
	// private static int query(int index) {
	// int sum = 0;
	// for (; index > 0; index -= (index & (-index))) {
	// sum += BIT[index];
	// }
	// return sum;
	// }
	//
	// private static void update(int size, int index, int val) {
	// for (; index <= size; index += (index & (-index))) {
	// BIT[index] += val;
	// }
	// }

	/*
	 * 
	 * tutorial :
	 * https://helloacm.com/algorithms-series-0-1-backpack-dynamic-programming-
	 * and-backtracking/
	 * 
	 */

	// here arr and prob zero based index
	// static int backPack(int n, int m, int[] arr, double[] prob, double p) {
	// double dp[][] = new double[n + 1][m + 1];
	// for (int i = 0; i <= n; ++i) {
	// dp[i][0] = 1.0;
	// }
	// for (int i = 1; i <= n; i++) {
	// for (int j = 1; j <= m; j++) {
	//
	// if (j < arr[i - 1]) { // insufficient capacity
	// dp[i][j] = dp[i - 1][j];
	// } else {
	// dp[i][j] = Math.max(dp[i - 1][j], dp[i - 1][j - arr[i - 1]] * (1.0 -
	// prob[i - 1]));
	// }
	//
	// }
	// }
	// for (int i = m; i >= 0; i--) { // reverse checking the maximum weight
	// if ((1.0 - dp[n][i]) <= p) {
	// return i;
	// }
	// }
	// return 0;
	// }

	// here arr and prob one based index
	// static int backPack1(int n, int m, int[] arr, double[] prob, double p) {
	//
	// double dp[] = new double[m + 1];
	//
	// dp[0] = 1.0;
	// for (int i = 1; i <= n; i++) {
	// for (int j = m; j >= arr[i]; --j) {
	// // dp[j] = dp[j] || dp[j - A[i - 1]];
	// dp[j] = Math.max(dp[j], dp[j - arr[i]] * (1.0 - prob[i]));
	// }
	// }
	// for (int i = m; i >= 0; i--) {
	// if (1.0 - dp[i] <= p) {
	// return i;
	// }
	// }
	// return 0;
	// }

	/*
	 *
	 * tutorial :
	 * https://www.hackerearth.com/practice/algorithms/searching/ternary-search/
	 * tutorial/
	 *
	 */

	// lightoj -> 1146
	// static double ternary(Point a, Point b, Point c, Point d) {
	//
	// double l = 0;
	// double r = 1;
	//
	// for (int i = 0; i < 200; i++) {
	// double mid1 = l + ((r - l) / 3);
	// double mid2 = r - ((r - l) / 3);
	//
	// double dis1 = func(a, b, c, d, mid1);
	// double dis2 = func(a, b, c, d, mid2);
	//
	// if(dis1 > dis2){
	// l = mid1;
	//
	// }
	// else{
	// r = mid2;
	// }
	// }
	//
	// return l;
	//
	// }
	//
	// static double func(Point a, Point b, Point c, Point d, double multiple) {
	//
	// double xDifAB = b.x - a.x;
	// double yDifAB = b.y - a.y;
	// double xDifCD = d.x - c.x;
	// double yDifCD = d.y - c.y;
	//
	// double x1 = a.x + xDifAB * multiple;
	// double y1 = a.y + yDifAB * multiple;
	// double x2 = c.x + xDifCD * multiple;
	// double y2 = c.y + yDifCD * multiple;
	//
	// double distance = Math.sqrt(((x1 - x2) * (x1 - x2)) +
	// ((y1 - y2) * (y1 - y2)));
	//
	// return distance;
	// }
	//
	// static class Point{
	// double x;
	// double y;
	//
	// Point(double x, double y){
	// this.x = x;
	// this.y = y;
	// }
	// }

	// static void primeFactorization(int n) {
	// int temp = n;
	// Map<Integer, Integer> map = new HashMap<Integer, Integer>();
	// for (int i = 2; i <= Math.sqrt(n); i++) {
	// if (n % i == 0) {
	// int count = 0;
	// while (n % i == 0) {
	// count++;
	// n = n / i;
	// }
	// System.out.println("i: " + i + ", count: " + count);
	// map.put(i, count);
	// }
	//
	// }
	// if (n != 1) {
	// System.out.println(n);
	// map.put(n, 1);
	// }
	//
	//// calculateSumOfDivisor(map, temp);
	// }

	// static int counter[] = new int[MAX];
	//
	// private static void calculateSumOfDivisor(Map<Integer, Integer> map, int
	// n) {
	// int sum = 1;
	// for(Integer key : map.keySet()){
	// int count = map.get(key);
	// sum *= ((Math.pow(key, count + 1) - 1) / (key - 1));
	// }
	// if(sum < MAX){
	// if(counter[sum] < n){
	//// System.out.println("H");
	// counter[sum] = n;
	// }
	//
	// }
	//
	//// System.out.println(sum);
	// }

	// static int phi[] = new int[MAX];
	// static int phiStepCount[] = new int[MAX];
	// static void computeTotient() {
	//
	// // Create and initialize an array to store
	// // phi or totient values
	// for (int i = 1; i < MAX; i++) {
	// phi[i] = i; // indicates not evaluated yet
	// // and initializes for product
	// // formula.
	// }
	//
	// // Compute other Phi values
	// for (int p = 2; p < MAX; p++) {
	//
	// // If phi[p] is not computed already,
	// // then number p is prime
	// if (phi[p] == p) {
	//
	// // Phi of a prime number p is
	// // always equal to p-1.
	// phi[p] = p - 1;
	//
	// // Update phi values of all
	// // multiples of p
	// for (int i = 2 * p; i < MAX; i += p) {
	//
	// // Add contribution of p to its
	// // multiple i by multiplying with
	// // (1 - 1/p)
	// phi[i] = (phi[i] / p) * (p - 1);
	// }
	//
	// // for (int i = p; i < MAX; i += p) {
	// //
	// // phi[i] -= (phi[i] / p);
	// // }
	//
	// }
	//// phiStepCount[p] = phiStepCount[phi[p]] + 1;
	// }
	//
	//// for(int i = 1; i < MAX; i++){
	//// phiStepCount[i] += phiStepCount[i - 1];
	//// }
	// }

	// public static BigInteger floorOfNthRoot(BigInteger x, int n) {
	// int sign = x.signum();
	// if (n <= 0 || (sign < 0))
	// throw new IllegalArgumentException();
	// if (sign == 0)
	// return BigInteger.ZERO;
	// if (n == 1)
	// return x;
	// BigInteger a;
	// BigInteger bigN = BigInteger.valueOf(n);
	// BigInteger bigNMinusOne = BigInteger.valueOf(n - 1);
	// BigInteger b = BigInteger.ZERO.setBit(1 + x.bitLength() / n);
	// do {
	// a = b;
	// b = a.multiply(bigNMinusOne).add(x.divide(a.pow(n - 1))).divide(bigN);
	// } while (b.compareTo(a) == -1);
	// return a;
	// }

	// O(log(max(A, B))).
	// static long gcd(long a, long b) {
	// if (b == 0)
	// return a;
	// return gcd(b, a % b);
	// }

	private static double getDistance(double x1, double y1, double x2, double y2) {

		return Math.sqrt(Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2));
	}

	// private static int getDecimal(String str) {
	// int val = 0;
	//
	// for (int i = str.length() - 1, j = 0; i >= 0; i--, j++) {
	// if (str.charAt(i) == '1') {
	// val += Math.pow(2, j);
	// }
	// }
	// return val;
	// }

	// private static int call(int i, int j, int[][] colors) {
	//
	// if (i >= colors.length) {
	// return 0;
	// }
	//
	// if (dp[i][j] != -1) {
	// return dp[i][j];
	//
	// }
	//
	// int result = Integer.MAX_VALUE;
	//
	// for (int k = 0; k < 3; k++) {
	// if (k == j) {
	// continue;
	// } else {
	// result = Math.min(result, call(i + 1, k, colors) + colors[i][j]);
	// }
	// }
	//
	// return dp[i][j] = result;
	// }

	// static int dp[][];

	// private static BigInteger fac(int n, int mod) {
	//
	// if (n <= 0) {
	// return BigInteger.ONE;
	// }
	// return BigInteger.valueOf(n).multiply(fac(n - 1, mod));
	// }

	// private static long modInverse(long n, long m){
	// return bigMod(n, m - 2, m);
	// }

	// private static long bigMod(long n, long k, long m) {
	//
	// long ans = 1;
	// while (k > 0) {
	// if ((k & 1) == 1) {
	// ans = (ans * n) % m;
	// }
	// n = (n * n) % m;
	// k >>= 1;
	// }
	// return ans;
	// }

	// Returns an iterator pointing to the first element
	// in the range [first, last] which does not compare less than val.
	// private static int lowerBoundNew(long[] arr, long num){
	// int start = 0;
	// int end = arr.length - 1;
	// int index = 0;
	// int len = arr.length;
	// int mid = 0;
	// while(true){
	// if(start > end){
	// break;
	// }
	// mid = (start + end) / 2;
	// if(arr[mid] > num){
	// end = mid - 1;
	// }
	// else if(arr[mid] < num){
	// start = mid + 1;
	// }
	// else{
	// while(mid >= 0 && arr[mid] == num){
	// mid--;
	// }
	// return mid + 1;
	// }
	// }
	// if(arr[mid] < num){
	// return mid + 1;
	// }
	// return mid;
	// }

	// upper_bound() is a standard library function
	// in C++ defined in the header .
	// It returns an iterator pointing to
	// the first element in the range [first, last)
	// that is greater than value, or last if no such element is found
	// private static int upperBoundNew(long[] arr, long num){
	//
	// int start = 0;
	// int end = arr.length - 1;
	// int index = 0;
	// int len = arr.length;
	// int mid = 0;
	// while(true){
	// if(start > end){
	// break;
	// }
	// mid = (start + end) / 2;
	// if(arr[mid] > num){
	// end = mid - 1;
	// }
	// else if(arr[mid] < num){
	// start = mid + 1;
	// }
	// else{
	// while(mid < len && arr[mid] == num){
	// mid++;
	// }
	// if(mid == len - 1 && arr[mid] == num){
	// return mid + 1;
	// }
	// else{
	// return mid;
	// }
	// }
	// }
	// if(arr[mid] < num){
	// return mid + 1;
	// }
	// return mid;
	// }

	// private static int upperBound(long[] arr, long num) {
	//
	// int start = 0;
	// int end = arr.length;
	//
	// int mid = 0;
	// int index = 0;
	// while (true) {
	//
	//// System.out.println(start + " " + end);
	// if (start > end) {
	// break;
	// }
	// mid = (start + end) / 2;
	// if (arr[mid] > num) {
	// end = mid - 1;
	//
	// } else if (arr[mid] < num) {
	// start = mid + 1;
	// } else {
	// return mid;
	// }
	//
	//// System.out.println("a: " + start + " " + end);
	// }
	//
	// // System.out.println(mid);
	// if (arr[mid] < num) {
	// index = mid + 1;
	// } else {
	// index = mid;
	// }
	// return index;
	// }

	static class InputReader {
		public BufferedReader reader;
		public StringTokenizer tokenizer;

		public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream));
			tokenizer = null;
		}

		public String next() {
			try {
				while (tokenizer == null || !tokenizer.hasMoreTokens()) {
					tokenizer = new StringTokenizer(reader.readLine());

				}
			} catch (IOException e) {
				return null;
			}
			return tokenizer.nextToken();
		}

		public String nextLine() {
			String line = null;
			try {
				tokenizer = null;
				line = reader.readLine();
			} catch (IOException e) {
				throw new RuntimeException(e);
			}
			return line;
		}

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

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

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

		public boolean hasNext() {
			try {
				while (tokenizer == null || !tokenizer.hasMoreTokens()) {
					tokenizer = new StringTokenizer(reader.readLine());
				}
			} catch (Exception e) {
				return false;
			}
			return true;
		}
	}
}