#include<bits/stdc++.h>
using namespace std;
int main(){
    string s="abcdefghijklmnopqrstuvwxyz",t;
    cin >> t;
    for(int i=0; i<26; i++){
        if(s[i]!=t[i]){
            cout << s[i] << "to" << t[i] << endl;
            break;
            
        }
    }
}