package main

import "fmt"

func csum(n int) (r int) {
	for n > 0 {
		r += n % 10
		n /= 10
	}
	return r
}

func main() {
	var n int
	fmt.Scan(&n)
	an := n
	for i := 2; i < 100; i++ {
		an1 := csum(an)
		an = an1
	}
	fmt.Println(an)
}