#include <bits/stdc++.h>

using namespace std;

int main() {
    string s;
    cin >> s;

    string t = "abcdefghijklmnopqrstuvwxyz";
    for (int i = 0; i < 26; ++i) {
        if (s[i] != t[i]) {
            cout << t[i] << "to" << s[i] << endl;
            return 0;
        }
    }
}