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