#include <map>
#include <set>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cctype>
#include <cstdio>
#include <limits>
#include <string>
#include <vector>
#include <cassert>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iomanip>
#include <numeric>
#include <sstream>
#include <utility>
#include <iostream>
#include <algorithm>
#include <functional>

#define stop exit(0)
#define nc -1
#define eps 1e-10
#define inf 1000000000
#define mod 1000000007
#define mp make_pair

#define fill(array,value) memset(array,value,sizeof(array))
#define f(i,beg,end) for(int i=beg; i<=end; i++)
#define F(i,beg,end) for(int i=beg; i>=end; i--)
#define Max(a,b) ( (a>b)?a:b )
#define Min(a,b) ( (a<b)?a:b )
#define pi 3.1415926535897932384626433832
#define iread(var) scanf("%d",&var)
#define dread(var) scanf("%f",&var)
#define lread(var) scanf("%lld",&var)
#define input(name) freopen(name,"r",stdin)
#define output(name) freopen(name,"w",stdout)
typedef unsigned long long ull;
typedef unsigned int ui;
typedef long double ld;
typedef long long ll;

using namespace std;

int n;
string a[1024], b[1024];
set <string> s;

void init()
{
    cin >> n;
    cin.ignore();

    f(i,1,n)
    {
        cin >> a[i];
        s.insert(a[i]);
        b[i] = a[i];
        sort(b[i].begin(),b[i].end());
    }

    f(i,2,n)
        if (b[i] != b[i-1])
        {
            cout << -1 << endl;
            return;
        }

    string ans = b[1];
    bool ok = true;

    f(i,1,n)
        if (a[i]==ans)
        {
            ok = false;
        }

    if (ok)
    {
        cout << ans << endl;
        return;
    }

    while (true)
    {
        next_permutation(ans.begin(),ans.end());
        if (s.find(ans)==s.end())
        {
            cout << ans << endl;
            return;
        }
    }
}

void solve()
{

}

int main()
{
//	input("test.txt");
    input("anagrams.in");
    output("anagrams.out");

	int numberOfTests = 1;
//	cin >> numberOfTests;

	f(i,1,numberOfTests)
	{
		init();
		solve();
	}

	return 0;
}