package main

import (
	"fmt"
)

func main() {
	var S string
	fmt.Scan(&S)

	m := map[rune]bool{}
	for _, v := range S {
		m[v] = true
	}
	for _, v := range "yukicoder" {
		if !m[v] {
			fmt.Printf("%c\n", v)
			break
		}
	}
}