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.util.ArrayList;
import java.util.LinkedList;
import java.util.StringTokenizer;

public class CodeForces {
    static reader input = new reader();
    static PrintWriter output = new PrintWriter(System.out);

    public static void main(String[] args) throws IOException {
        /*
        BufferedReader bf = new BufferedReader(new FileReader("input.txt"));
        PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter("output.txt")));
        StringTokenizer stk= new StringTokenizer(bf.readLine());;
        int n=Integer.parseInt(stk.nextToken());
        */
        C();
        output.close();
    }

    public static void A(){

    }

    public static void B(){

    }

    public static void C(){
        int n=input.nextInt();
        String arr[]=new String[n];
        ArrayList<ArrayList<Integer>> graph=new ArrayList<>();
        for(int i=0;i<26;i++){
            graph.add(new ArrayList<>());
        }
        for(int i=0;i<n;i++){
            arr[i]=input.next();
        }
        for(int i=0;i<n-1;i++) {
            String x = arr[i];
            String y = arr[i + 1];
            int j = 0, k = 0,xlen=x.length(),ylen=y.length();
            while(j<xlen&&k<ylen){
                if(x.charAt(j)!=y.charAt(k)){
                    graph.get(x.charAt(j)-'a').add(y.charAt(k)-'a');
                    break;
                }
                j++;
                k++;
            }
            if(k==ylen) {
                output.println("Impossible");
                return;
            }
        }
        StringBuilder ans=new StringBuilder("");
        if(helper(graph,ans))
            output.println(ans);
        else
            output.println("Impossible");
    }

    public static boolean helper(ArrayList<ArrayList<Integer>>graph,StringBuilder ans){
        int indegree[]=new int[26];
        LinkedList<Integer>q=new LinkedList<>();
        for(int i=0;i<26;i++){
            for(int j:graph.get(i)){
                indegree[j]++;
            }
        }
        for(int i=0;i<26;i++){
            if(indegree[i]==0)
                q.add(i);
        }
        while(!q.isEmpty()){
            int x=q.removeFirst();
            ans.append((char)(x+'a'));
            for(int j:graph.get(x)){
                indegree[j]--;
                if(indegree[j]==0)
                    q.add(j);
            }
        }
        if(ans.length()==26)
            return true;
        else
            return false;
    }

    public static void D(){

    }

    public static void E(){

    }

    public static void F(){

    }

    public static long factorial(int a){
        long ans=1;
        for(int i=1;i<=a;i++){
            ans*=i;
        }
        return ans;
    }
    public static long LCM(long a,long b){
        return (a*b)/GCD(a,b);
    }
    public static long GCD(long a,long b){
        if(a==0)
            return b;
        else if(b==0)
            return a;
        else
            return GCD(b%a,a);
    }

    public static boolean isPrime(long num){
        if(num==1)
            return false;
        else if(num==2||num==3)
            return true;
        else if(num%2==0||num%3==0)
            return false;
        else{
            for(long i=5;i*i<=num;i+=6){
                if(num%i==0||num%(i+2)==0)
                    return false;
            }
        }
        return true;
    }

    public static ArrayList<Integer> SieveofEratothenis(){
        ArrayList<Integer>ans=new ArrayList<>();
        boolean visited[]=new boolean[1000000];
        for(int i=2;i<1000000;i++){
            if(!visited[i]){
                ans.add(i);
                for(long j=(long)i*i;j<1000000;j+=i){
                    visited[(int)j]=true;
                }
            }
        }
        return ans;
    }

    public static void mergesort(long arr[],int start,int end){//start and end must be indexes
        if(start<end) {
            int mid=(start+end)/2;
            mergesort(arr,start,mid);
            mergesort(arr, mid+1, end);
            merge(arr, start,mid,end);
        }
    }
    public static void merge(long arr[],int start,int mid,int end){
        int lsize=mid-start+1,rsize=end-mid;
        long l[]=new long[lsize],r[]=new long[rsize];
        for(int i=start;i<=mid;i++){
            l[i-start]=arr[i];
        }
        for(int i=mid+1;i<=end;i++){
            r[i-mid-1]=arr[i];
        }
        int i=0,j=0,k=start;
        while(i<lsize&&j<rsize){
            if(l[i]<=r[j]){
                arr[k++]=l[i++];
            }else{
                arr[k++]=r[j++];
            }
        }
        while(i<lsize)
            arr[k++]=l[i++];
        while(j<rsize)
            arr[k++]=r[j++];
    }
}

class Value{
    int ans;
    Value(int ans)
    {
        this.ans=ans;
    }
}

class Triple{
    int num,size,money;
    Triple(int num,int size,int money){
        this.num=num;
        this.size=size;
        this.money=money;
    }
}

class Pair{
    int num, size;
    Pair(int num,int size){
        this.size=size;
        this.num=num;
    }
}

class Op{
    int op,count;
    char dir;
    public Op(int op){
        this.op=op;
    }
}

class reader {
    BufferedReader br;
    StringTokenizer st;

    public reader() {
        br = new BufferedReader(new
                InputStreamReader(System.in));
    }

    String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.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());
    }

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

    public int[] nextIntArray(int arraySize) {
        int array[] = new int[arraySize];
        for (int i = 0; i < arraySize; i++) {
            array[i] = nextInt();
        }
        return array;
    }

    public long[] nextLongArray(int arraySize) {
        long array[] = new long[arraySize];
        for (int i = 0; i < arraySize; i++) {
            array[i] = nextLong();
        }
        return array;
    }
}