#include <stdio.h>

int main(void)
{
	char a[] = "abcdefghijklmnopqrstuvwxyz";
	char s[27];
	int i;

	scanf("%s", s);

	for (i = 0; i < 26; i++) {
		if (s[i] != a[i])
			break;
	}

	printf("%cto%c\n", a[i], s[i]);

	return 0;
}