package main

import "fmt"

func main() {

	var S string
	fmt.Scan(&S)

	var T string
	T = "abcdefghijklmnopqrstuvwxyz"

	for i := 0; i < len(S); i++ {
		if S[i] != T[i] {
			fmt.Printf("%cto%c\n", T[i], S[i])
			break
		}
	}
}