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

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