#include<iostream>
#include<string>

using namespace std;

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