#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef long double ld;
typedef pair<int,int> P;

int main() {
  string s;
  cin >> s;
  string res = "";
  for (int i = 0; i < 26; i++) {
    if (char('a' + i) != s[i]) {
      cout << char('a' + i);
      cout << "to";
      cout << s[i] << endl;
      break;
    }
  }
  return 0;
}