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.util.*;
import java.io.*;
import java.math.BigInteger;
import java.text.*;
public class Main {
    static long mod = 1000_000_007;
    static long mod1 = 998244353;
    static boolean fileIO = false;
    static boolean memory = true;
    static FastScanner f;
    static PrintWriter pw;
    static double eps = (double)1e-6;
    static int maxN = (int)1e6;
 
    // N = 1 or N = max ?
    // longs vs. ints ?
    // max / min ?

    static int n , topS[] , itr;
    static String s[];
    static ArrayList<Integer> adj[];
    static boolean vis[] , ok;

    static int inD[];

    public static void solve() throws Exception {
        n = f.ni();
        s = new String[n];
        adj = new ArrayList[26];
        topS = new int[26];
        itr = 0;
        inD = new int[26];
        vis = new boolean[26];
        for (int i = 0; i < 26; ++i) adj[i] = new ArrayList<>();          
        ok = true;
        
        for (int i = 0; i < n; ++i) s[i] = f.next();

        // abdc
        // abcd
        for (int i = 0; i + 1 < n; ++i) {
            String a = s[i];
            String b = s[i + 1];
            int l = Math.min(a.length() , b.length());
            if(a.substring(0, l).equals(b.substring(0, l))){
                if(b.length() < a.length()){
                    pn("Impossible");
                    return;
                }
                else continue;
            }
            for(int j = 0; j < l; ++j){
                if(a.charAt(j) == b.charAt(j)) continue;
                int u = a.charAt(j) - 'a';
                int v = b.charAt(j) - 'a';
                adj[u].add(v);
                ++inD[v];
                break;
            }
        }

        Queue<Integer> q = new LinkedList<>();
        
        for (int i = 0; i < 26; ++i) {
            if (inD[i] == 0) q.add(i);
        }

        StringBuffer ans = new StringBuffer("");
        while (q.size() > 0) {
            int u = q.poll();
            ans.append((char)(u + 'a'));
            for (Integer v : adj[u]) {
                if (--inD[v] == 0) q.add(v);
            }
        }

        pn(ans.length() < 26 ? "Impossible" : ans);
    }   
 
    public static void main(String[] args)throws Exception {
        if(memory) new Thread(null, new Runnable() {public void run(){try{new Main().run();}catch(Exception e){e.printStackTrace();System.exit(1);}}}, "", 1 << 28).start();
        else new Main().run();
    }
        
/******************************END OF MAIN PROGRAM*******************************************/
    void run()throws Exception {
        if (System.getProperty("ONLINE_JUDGE") == null) {
            f = new FastScanner("");
            pw = new PrintWriter(System.out);
        }
        else {
            f = new FastScanner();
            pw = new PrintWriter(System.out);
            //fw = new FileWriter("!out.txt");
        }
        //pre();
        int t = 1;
        int tt = 1;
        while(t --> 0) {
            //fw.write("Case #" + (tt++) + ": ");
            //fw.write("\n");
            solve();
        }
        pw.flush(); 
        pw.close(); 
    }
 
    public static class FastScanner {
        BufferedReader br;
        StringTokenizer st;
 
        public FastScanner(String str) throws Exception {
            try {
                br = new BufferedReader(new FileReader("!a.txt"));
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        }
 
        public FastScanner() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }
 
        public String next()throws IOException {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        }
 
        public int ni() throws IOException {return Integer.parseInt(next());}
 
        public long nl() throws IOException {return Long.parseLong(next());}
 
        public String nextLine() throws IOException {return br.readLine();}
 
        public double nd() throws IOException {return Double.parseDouble(next());}
 
    }
 
    public static void pn(Object... o) {for(int i = 0; i < o.length; ++i) pw.print(o[i] + (i + 1 < o.length ? " ": "\n"));}
    public static void p(Object... o) {for(int i = 0; i < o.length; ++i) pw.print(o[i] + (i + 1 < o.length ? " " : ""));}
    public static void pni(Object... o) {for(Object obj : o) pw.print(obj + " "); pw.println(); pw.flush();}
    public static int gcd(int a,int b){if(b==0)return a;else{return gcd(b,a%b);}}
    public static long gcd(long a,long b){if(b==0l)return a;else{return gcd(b,a%b);}}
    public static long lcm(long a,long b){return (a*b/gcd(a,b));}
    public static long pow(long a,long b){long res=1;while(b>0){if((b&1)==1)res=res*a;b>>=1;a=a*a;}return res;}
    public static int pow(int a,int b){int res=1;while(b>0){if((b&1)==1)res=res*a;b>>=1;a=a*a;}return res;}
    public static long mpow(long a,long b, long m){long res=1;while(b>0){if((b&1)==1)res=((res%m)*(a%m))%m;b>>=1;a=((a%m)*(a%m))%m;}return res;}
    public static long mul(long a , long b , long mod){return ((a%mod)*(b%mod)%mod);}
    public static long adp(long a , long b){return ((a%mod)+(b%mod)%mod);}
    public static int dig(long a){int cnt=0;while(a>0){a/=10;++cnt;}return Math.max(1,cnt);}
    public static int dig(int a){int cnt=0;while(a>0){a/=10;++cnt;}return Math.max(1,cnt);}
    public static boolean isPrime(long n){if(n<=1)return false;if(n<=3)return true;if(n%2==0||n%3==0)return false;for(long i=5;i*i<=n;i=i+6)if(n%i==0||n%(i+2)==0)return false;return true;}
    public 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;}
    public static HashSet<Long> factors(long n){HashSet<Long> hs=new HashSet<Long>();for(long i=1;i<=(long)Math.sqrt(n);i++){if(n%i==0){hs.add(i);hs.add(n/i);}}return hs;}
    public static HashSet<Integer> factors(int n){HashSet<Integer> hs=new HashSet<Integer>();for(int i=1;i<=(int)Math.sqrt(n);i++){if(n%i==0){hs.add(i);hs.add(n/i);}}return hs;}
    public static HashSet<Long> pf(long n){HashSet<Long> ff=factors(n);HashSet<Long> ans=new HashSet<Long>();for(Long i:ff)if(isPrime(i))ans.add(i);return ans;}
    public static HashSet<Integer> pf(int n){HashSet<Integer> ff=factors(n);HashSet<Integer> ans=new HashSet<Integer>();for(Integer i:ff)if(isPrime(i))ans.add(i);return ans;}
    public static int gnv(char c){return Character.getNumericValue(c);}
    public static void sort(int[] a){ArrayList<Integer> l=new ArrayList<>();for(int i:a)l.add(i);Collections.sort(l);for(int i=0;i<a.length;++i)a[i]=l.get(i);}
    public static void sort(long[] a){ArrayList<Long> l=new ArrayList<>();for(long i:a)l.add(i);Collections.sort(l);for(int i=0;i<a.length;++i)a[i]=l.get(i);}
    public static void sort(ArrayList<Integer> a){Collections.sort(a);}
}