#include <bits/stdc++.h>
using namespace std;

int i, n;
string a[105];

bool check(int x) {
  int who[105];
  memset(who, 0, sizeof(who));

  who[0] = 1;
  for(int i = 0; i < a[x].size(); ++i) {
    if(!who[i]) continue;

    for(int j = 1; j <= n; ++j) {
      if(j == x) continue;

      bool ok = 1;
      for(int k = 0; k < a[j].size() && ok; ++k)
        if(a[j][k] != a[x][i + k]) ok = 0;

      if(ok) who[i + a[j].size()] = 1;
    }
  }

  return who[a[x].size()];
}

int main() {
  ios_base::sync_with_stdio(0);

  cin >> n;
  for(i = 1; i <= n; ++i) cin >> a[i];

  sort(a + 1, a + n + 1, [](string a, string b) { return a.size() < b.size(); });

  reverse(a + 1, a + n + 1);

  for(i = 1; i <= n; ++i)
    if(check(i)) return cout << a[i] << '\n', 0;

  cout << "-1\n";

  return 0;
}