#include<iostream>
using namespace std;
int main()
{
int n;
while(cin>>n,n)
{
string s[201];
int min=201;
for(int x=0;x<n;x++)
{
cin>>s[x];
min=min>(int)s[x].size()? s[x].size():min;
}
while(min)
{
int j=1;
while(j<n)
{
if(s[0].substr(s[0].size()-min,min)!=s[j].substr(s[j].size()-min,min)) break;
j++;
}
if(j==n)
{
cout<<s[0].substr(s[0].size()-min,min)<<endl;
break;
}
min--;
}
if(min==0) cout<<" "<<endl;
}
}