#include<bits/stdc++.h>
using namespace std;
#define line cout<<"------------"<<endl
const int N = 33;

map<string, int>mp,vis;
map<int, string>ms;
vector<string>ve;
int n;
string s,u, str;
bool cmp(string a, string b){
    if(a.length() != b.length()) return a.length() > b.length();
    else return a < b;
}
void change(int pos){
    str.clear();
    string temp = s.substr(pos);
    str += temp;
    temp = s.substr(0,pos);
    str += temp;
}
int main(){
    while(scanf("%d",&n)!=EOF){
        mp.clear();
        ve.clear();
        int nn = n;
        while(nn--){
            vis.clear();
            cin >> s;
            int len = s.length();
            for(int k=0; k<len; k++){
                change(k);
                for(int i=1;i < (1<<len); i++){
                    for(int j=0; j<len; j++){
                        if(i >> j & 1) {
                           u += str[j];
                        }
                    }
                    if(vis[u] == 0){
                       mp[u]++;
                       vis[u] = 1;
                    }
                    u.clear();
                }
            }
        }
        int flag=0;
        for(auto i: mp) {
            if(i.second == n){
                ve.push_back(i.first);
                flag = 1;
            }
        }
        sort(ve.begin(),ve.end(),cmp);
        if(flag == 0)
            printf("0\n");
        else cout << ve[0] << endl;
    }
    return 0;
}