#include <bits/stdc++.h>
using namespace std;
/* typedef */
typedef long long ll;
typedef pair<int, int> pii;
/* constant */
const int INF = 1 << 30;
const ll LINF = 1LL << 50;
const int NIL = -1;
const int MAX = 10000;
const int mod = 1000000007;
const double pi = 3.141592653589;
/* global variables */
/* function */
/* main */
int main(){
    string S;
    cin >> S;
    string alpha = "";
    for (int i = 0; i < 26; i++) {
        string s;
        s = (char) 'a' + i;
        alpha += s;
    }

    for (int i = 0; i < 26; i++) {
        if (S[i] != alpha[i]) {
            cout << alpha[i] << "to" << S[i] << '\n';
            break;
        }
    }
}