package main

import (
	"fmt"
)

func main() {
	val := make([]int, 11)
	var v int
	for i := 0; i < 9; i++ {
		fmt.Scan(&v)
		val[v] = 1
	}

	for i, v := range val {
		if i > 0 && v == 0 {
			fmt.Println(i)
			break
		}
	}
}