#include <bits/stdc++.h>

using namespace std;

using ll = long long;

constexpr char newl = '\n';

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    string s;
    cin >> s;

    string s2 = "abcdefghijklmnopqrstuvwxyz";
    for (int i = 0; i < 26; i++) {
        if (s[i] != s2[i]) {
            cout << s2[i] << "to" << s[i] << newl;
            break;
        }
    }

    return 0;
}