#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int n;
    cin >> n;
    vector<vector<int>> vs(n, vector<int>(26));
    vector<string> s(n);
    rep(i,n) {
        cin >> s[i];
        for(char c : s[i]) {
            vs[i][c-'a']++;
        }
    }
    rep(i,n) {
        int cnt = 0;
        rep(j,n) {
            if(i==j) continue;
            bool ok = false;
            for(int k=0;k<26;k++) {
                if(vs[i][k]<vs[j][k]) ok = true;
            }
            cnt += ok;
        }
        if(cnt==n-1) {
            cout << s[i] << endl;
            return 0;
        }
    }
    cout<<-1<<endl;
    return 0;
}