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