#include <stdio.h>

int main()
{
	char box1[26];
	char box2[] ="abcdefghijklmnopqrstuvwxyz";

	scanf("%s", box1);

	for(int i; i < 26; i++)
	{
		if(box1[i] != box2[i])
		{
			printf("%cto%c\n", box1[i], box2[i]);
			return 0;
		}
		else
		{

		}
	}

	return 0;
}