#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n;
  cin >> n;
  vector<string> s(n);
  rep(i, n) cin >> s[i];
  string ans = "";
  rep(i, n) ans += s[i][i] ^ 'a' ^ 'b';
  cout << ans << endl;
  return 0;
}