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.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.LinkedList;
import java.util.Queue;
import java.util.StringTokenizer;
 
 
public class Solution{
    
    ///////////////////////////////////////////////////////////////////////////
    static class FastScanner{
        BufferedReader s;
        StringTokenizer st;
        
        public FastScanner(InputStream InputStream){
            st = new StringTokenizer("");
            s = new BufferedReader(new InputStreamReader(InputStream));
        }
        
        public FastScanner(File f) throws FileNotFoundException{
            st = new StringTokenizer("");
            s = new BufferedReader (new FileReader(f));
        }
        
        public int nextInt() throws IOException{
            if(st.hasMoreTokens())
                return Integer.parseInt(st.nextToken());
            else{
                st = new StringTokenizer(s.readLine());
                return nextInt();
            }
        }
        
        public BigInteger big() throws IOException{
            if(st.hasMoreTokens())
                return new BigInteger(st.nextToken());
            else{
                st = new StringTokenizer(s.readLine());
                return big();
            }
        }
        
        public double nextDouble() throws IOException{
            if(st.hasMoreTokens())
                return Double.parseDouble(st.nextToken());
            else{
                st = new StringTokenizer(s.readLine());
                return nextDouble();
            }
        }
      
        public long nextLong() throws IOException{
            if(st.hasMoreTokens())
                return Long.parseLong(st.nextToken());
            else{
                st = new StringTokenizer(s.readLine());
                return nextLong();
            }
        }
        
        public String nextString() throws IOException{
            if(st.hasMoreTokens())
                return st.nextToken();
            else{
                st = new StringTokenizer(s.readLine());
                return nextString();
            }
            
        }
        public String readLine() throws IOException{
            return s.readLine();
        }
        
        public void close() throws IOException{
            s.close();
        }
        
    }
    
    ////////////////////////////////////////////////////////////////////
    //      Number Theory
    
    long pow(long a,long b,long mod){
        long x = 1; long y = a;
        while(b > 0){
            if(b % 2 == 1){
                x = (x*y);
                x %= mod;
            }
            y = (y*y);
            y %= mod;
            b /= 2;         
        }
        return x;
    }
    
    int divisor(long x,long[] a){
        long limit = x;
        int numberOfDivisors = 0;
 
        for (int i=1; i < limit; ++i) {
            if (x % i == 0) {
                limit = x / i;
                if (limit != i) {
                    numberOfDivisors++;
                }
                numberOfDivisors++;
            }
        }
        return numberOfDivisors;
    }
    
    void findSubsets(int array[]){
        long numOfSubsets = 1 << array.length; 
        for(int i = 0; i < numOfSubsets; i++){    
            @SuppressWarnings("unused")
            int pos = array.length - 1;
            int bitmask = i;
            while(bitmask > 0){     
                if((bitmask & 1) == 1)
//                    ww.print(array[pos]+" ");
                bitmask >>= 1;
                pos--;
            }
//            ww.println();
        }
    }
    
    
    public static long gcd(long a, long b){
        return b == 0 ? a : gcd(b,a%b);
    }
    
  
    public static int lcm(int a,int b, int c){
        return lcm(lcm(a,b),c);
    }
    
    public static int lcm(int a, int b){
        return (int) (a*b/gcd(a,b));
    }
    
    public static long invl(long a, long mod) {
        long b = mod;
        long p = 1, q = 0;
        while (b > 0) {
            long c = a / b;
            long d;
            d = a;
            a = b;
            b = d % b;
            d = p;
            p = q;
            q = d - c * q;
        }
        return p < 0 ? p + mod : p;
    }
    
    ////////////////////////////////////////////////////////////////////
    
    
//    FastScanner s = new FastScanner(new File("input.txt"));
//    PrintWriter ww = new PrintWriter(new FileWriter("output.txt"));
    static InputStream inputStream = System.in;
    static FastScanner s = new FastScanner(inputStream); 
    static OutputStream outputStream = System.out;
    static PrintWriter ww = new PrintWriter(new OutputStreamWriter(outputStream));
//      private static Scanner s = new Scanner(System.in);
    @SuppressWarnings("unused")
    private static int[][] states = { {-1,0} , {1,0} , {0,-1} , {0,1} };
    
      
    //////////////////////////////////////////////////////////////////// 
     
    
     
    public static void main(String[] args) throws IOException{
        new Solution().solve();
        s.close();
        ww.close();
    }
    
    
    ////////////////////////////////////////////////////////////////////
   
    
    void solve() throws IOException{
        
        int n = s.nextInt();
        String[] a = new String[n];
        for(int i=0;i<n;i++) a[i] = s.nextString();
        boolean[][] g = new boolean[26][26];
        boolean valid = true;
        
        for(int i=0;i<n;i++){
            for(int j=i+1;j<n;j++){
                for(int k=0;k<a[i].length() && k<a[j].length();k++){
                    if(a[i].charAt(k) != a[j].charAt(k)){
                        g[a[i].charAt(k)-'a'][a[j].charAt(k)-'a'] = true;
                        break;
                    }
                    if(k+1 == a[j].length()) valid = false;
                }
            }
        }
        
        // Transitive Closure
        for(int k=0;k<26;k++)
            for(int i=0;i<26;i++)
                for(int j=0;j<26;j++)
                    g[i][j] |= g[i][k] && g[k][j];
        
        //Cycle Detection
        for(int i=0;i<26;i++)
                valid &= !g[i][i];
        
        if(!valid) ww.println("Impossible");
        else{
            Queue<Integer> q = new LinkedList<Integer>();
            int[] d = new int[26];
            
            for(int i=0;i<26;i++)
                for(int j=0;j<26;j++)
                    if(g[i][j]) d[j]++;
            
            for(int i=0;i<26;i++) if(d[i] == 0) q.add(i);
            
            while(!q.isEmpty()){
                int in = q.poll();
                ww.print((char)(in+'a'));
                for(int i=0;i<26;i++){
                    if(g[in][i]){
                        d[i]--;
                        if(d[i] == 0) q.add(i);
                    }
                }
            }
            
        }
        
    }
}