#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
    string S;
    cin >> S;
    char x, y;
    for (int i = 0; i < 26; i++) {
        if (S[i] != 'a' + i) {
            x = 'a' + i;
            y = S[i];
            break;
        }
    }
    cout << x << "to" << y << "\n";
    return 0;
}