#include <iostream>
#include <algorithm>
#include <fstream>
using namespace std;
int main()
{
    freopen ( "anagrams.in", "r", stdin );
	freopen ( "anagrams.out", "w" , stdout );
    int n,i,flag=0;
    string s[1000]; char ch;
    cin>>n;
    cin.get(ch);
    for (i=0;i<n;i++)
    {
        cin>>s[i];
        sort (s[i].begin(),s[i].end());
        if ((i>0)&&(s[i]!=s[i-1])) flag=1;
    }
    if (flag==1) cout<<"-1"<<endl;
    else cout<<s[0]<<endl;
    return 0;
}