#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;


int main(){
    string alph = "abcdefghijklmnopqrstuvwxyz", s;
    cin >> s;
    for (int i=0; i < 26; i++){
        if (alph[i] != s[i]){
            cout << alph[i] << "to" << s[i] << endl;
            exit(0);
        }
    }
}