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

int main()
{
    string S;
    cin >> S;
    int i = 0;
    for (char s = 'a'; s <= 'z'; s++)
    {
        if (S[i] != s)
        {
            cout << s << "to" << S[i];
            return 0;
        }
        i++;
    }
}