#include <bits/stdc++.h>
using namespace std;


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

    char check = 'a';
    string ans;
    for (auto c : s){
        if (check != c){
            ans = check; 
            ans += "to";
            ans += c;
            break;
        }
        check += 1;
    }

    cout << ans << endl;
}