#include <iostream>
#include <string>
using namespace std;
int main()
{
	char *S1="abcdefghijklmnopqrstuvwxyz";
	string S;
	cin>>S;
	for (int i=0;i<26;i++){
		if (S1[i]!=S[i]){
			cout<<S1[i]<<"to"<<S[i]<<endl;
			return 0;
		}
	}

	return 0;
}