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;
public class cf1 {
    static long mod = (long)1e9 + 7;
    static long mod1 = 998244353;
    static FastScanner f;
    static PrintWriter pw = new PrintWriter(System.out);
    static Scanner S = new Scanner(System.in);
    static long x0; static long y0;
    static int inf = (int)(1e9) + 5;
    static long oo = (long)1e14 + 5;
    static double eps = (double)1e-9; 

    static boolean g[][];
    static int inD[];
    static void topS() {
        Queue<Integer> q = new LinkedList<>();
        String ans = "";

        for (int i = 0; i < 26; ++i) {
            for (int j = 0; j < 26; ++j) {
                if (g[i][j]) ++inD[j];
            }
        }

        for (int i = 0; i < 26; ++i) if (inD[i] == 0) q.add(i);

        while (q.size() > 0) {
            int s = q.poll();
            ans += (char)(s + 'a');
            for (int i = 0; i < 26; ++i) {
                if (g[s][i]) {
                    --inD[i];
                    if (inD[i] == 0) q.add(i);
                }
            }
        }

        pn(ans.length() < 26 ? "Impossible" : ans);
    }

    public static void solve() {
        int n = f.ni();

        String words[] = new String[n];

        for (int i = 0; i < n; ++i) {
            words[i] = f.next();
        }

        g = new boolean[26][26];
        inD = new int[26];

        for (int i = 0; i + 1 < n; ++i) {
            
            if (words[i].startsWith(words[i + 1]) && !words[i].equals(words[i + 1])) {
                pn("Impossible");
                return;
            }

            for (int j = 0; j < Math.min(words[i].length() , words[i + 1].length()); ++j) {
                if (words[i].charAt(j) != words[i + 1].charAt(j)) {
                    g[words[i].charAt(j) - 'a'][words[i + 1].charAt(j) - 'a'] = true;
                    break;
                }
            }
        }

        topS();
    }   

    public static void main(String[] args)throws NumberFormatException , IOException {   
        init();
        boolean tc = false;
        int t = tc ? f.ni() : 1;
        while(t --> 0) solve();
        pw.flush(); 
        pw.close();  
    }
        
/******************************END OF MAIN PROGRAM*******************************************/
    public static void init()throws IOException{if(System.getProperty("ONLINE_JUDGE")==null){f=new FastScanner("");}else{f=new FastScanner(System.in);}}
    public static class FastScanner {
        BufferedReader br;StringTokenizer st;
        FastScanner(InputStream stream){try{br=new BufferedReader(new InputStreamReader(stream));}catch(Exception e){e.printStackTrace();}}
        FastScanner(String str){try{br=new BufferedReader(new FileReader("!a.txt"));}catch(Exception e){e.printStackTrace();}}
        String next(){while(st==null||!st.hasMoreTokens()){try{st=new StringTokenizer(br.readLine());}catch(IOException e){e.printStackTrace();}}return st.nextToken();}
        String nextLine()throws IOException{return br.readLine();}int ni(){return Integer.parseInt(next());}long nl(){return Long.parseLong(next());}double nd(){return Double.parseDouble(next());}
    }
    public static void pn(Object o){pw.println(o);}
    public static void p(Object o){pw.print(o);}
    public static void pni(Object o){pw.println(o);pw.flush();}
    static int gcd(int a,int b){if(b==0)return a;else{return gcd(b,a%b);}}
    static long gcd(long a,long b){if(b==0l)return a;else{return gcd(b,a%b);}}
    static long lcm(long a,long b){return (a*b/gcd(a,b));}
    static long exgcd(long a,long b){if(b==0){x0=1;y0=0;return a;}long temp=exgcd(b,a%b);long t=x0;x0=y0;y0=t-a/b*y0;return temp;}
    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;}
    static long mpow(long a,long b){long res=1;while(b>0l){if((b&1)==1l)res=((res%mod)*(a%mod))%mod;b>>=1l;a=((a%mod)*(a%mod))%mod;}return res;}
    static long mul(long a , long b){return ((a%mod)*(b%mod)%mod);}
    static long adp(long a , long b){return ((a%mod)+(b%mod)%mod);}
    static int log2(int x){return (int)(Math.log(x)/Math.log(2));}
    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;}
    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;}
    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;}
    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;}
    static HashSet<Long> pf(long n){HashSet<Long> ff=factors(n);HashSet<Long> res=new HashSet<Long>();for(Long i:ff)if(isPrime(i))res.add(i);return res;}
    static HashSet<Integer> pf(int n){HashSet<Integer> ff=factors(n);HashSet<Integer> res=new HashSet<Integer>();for(Integer i:ff)if(isPrime(i))res.add(i);return res;}
    static int[] inpint(int n){int arr[]=new int[n+1];for(int i=1;i<=n;++i){arr[i]=f.ni();}return arr;}
    static long[] inplong(int n){long arr[] = new long[n+1];for(int i=1;i<=n;++i){arr[i]=f.nl();}return arr;}
    static boolean ise(int x){return ((x&1)==0);}static boolean ise(long x){return ((x&1)==0);}
    static int gnv(char c){return Character.getNumericValue(c);}//No. of integers less than equal to i in ub
    static int log(long x){return x==1?0:(1+log(x/2));} static int log(int x){return x==1?0:(1+log(x/2));}
    static int upperbound(int a[],int i){int lo=0,hi=a.length-1,mid=0;int count=0;while(lo<=hi){mid=(lo+hi)/2;if(a[mid]<=i){count=mid+1;lo=mid+1;}else hi=mid-1;}return count;}
    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);}
    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);}
    static void sort(ArrayList<Integer> a){Collections.sort(a);}//!Precompute fact in ncr()!
    static int nextPowerOf2(int n){int count=0;if(n>0&&(n&(n-1))==0)return n;while(n!=0){n>>=1;count += 1;}return 1<<count;} 
}