#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

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

    for (int i = 0; i < 26; i++) {
        char c = 'a' + i;
        if (s[i] != c) {
            cout << c << "to" << s[i] << endl;
            break;
        }
    }

    return 0;
}