#include <iostream>
using namespace std;
int main()
{
    while (true)
    {
        int n;
        cin>>n;
        if (n==0) break;
        else
        {
            string s[n];
            for (int i=0;i<n;i++) cin>>s[i];
            //cout<<x[2];

            int m=200;
            string a;

            for (int i=0;i<n;i++) if (s[i].size()<m) {m=s[i].size(); a=s[i];}
            //cout<<a;
            int p=0;
            int q=0;
            bool is_same=true;
            for (int i=m-1;i>=0;i--)
            {   q=q+1;
                for (int j=0;j<n;j++)
                {   
                    for (int k=(s[j].size()-q);k>=0;k--)
                    {
                        if (a[i]==s[j][k]) break;
                        else is_same=false;
                    }
                }
                if (is_same==true) p=p+1;
            }

            //cout<<p;
            for (int i=m-p;i<=m-1;i++)
            {
               cout<<a[i];
            }
            cout<<"\n";

        }
    }
    return 0;
}