#include <iostream>
#include <vector>
#include <string>
#include <cstdio>

using namespace std;

int main(){

    string s;
    cin>>s;

    string com="abcdefghijklmnopqrstuvwxyz";

    string ans;
    for(int i=0; i<26; i++){

        if (com[i]!=s[i]){
            cout<<com[i]<<"to"<<s[i]<<endl;
            break;
        }

    }
    
}