#include <vector>
#include <queue>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <string>
#include <sstream>
#include <iostream>
#include <fstream>
#include <functional>
#include <cmath>
#include <ctime>
#include <cstring>
#include <algorithm>
#include <windows.h>

#pragma warning( disable: 4996 )

using namespace std;

typedef unsigned long long ull;

template<typename T> inline T sqr(T a) { return a*a; }
template<typename T> inline int size(const T& c) { return (int)c.size(); }

#define zero(a) memset( &a, 0, sizeof(a) )

//#define printf
//#define DBG
//#define VERIFY
#define ERR         -1

#define INF         1000000

int n;
vector<string> v;
char s[40];

int main() {

    FILE *fin = fopen("anagrams.in", "r");
    FILE *fout = fopen("anagrams.out", "w+");
    int i;

    fscanf( fin, "%d\n", &n);

    for ( i = 0; i < n; i++ ) {

        fgets( s, 40, fin );
        s[strcspn(s, "\n")] = '\0';

        string ss = s;

        sort( ss.begin(), ss.end() );

        v.push_back( ss );
    }

    sort( v.begin(), v.end() );

    if ( v[0] == v[ n-1 ] ) {

        fprintf( fout, "%s", v[0].c_str() );
    } else {

        fprintf( fout, "-1" );
    }

    return 0;
}