#include <bits/extc++.h>

int main() {
  using namespace std;
  cin.tie(nullptr)->sync_with_stdio(false);
  string s;
  cin >> s;
  for (int i = 0; i < 26; ++i) {
    if (s[i] - 'a' != i) {
      cout << string(1, 'a' + i) + "to" + s[i] << '\n';
      exit(0);
    }
  }
}