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

int main() {
  string s;
  cin >> s;
  rep(i, s.size()) {
    if (s[i] != 'a' + i) {
      cout << char('a' + i) << "to" << s[i] << endl;
      return 0;
    }
  }
  return 0;
}