package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
)

func solve(in io.Reader, out, err io.Writer) {
	for i := 1; i < 11; i++ {
		temp := 0
		fmt.Fscan(in, &temp)
		if temp != i {
			fmt.Fprintln(out, i)
			break
		}
	}
}

func main() {
	br := bufio.NewReaderSize(os.Stdin, int(1e7))
	solve(br, os.Stdout, os.Stderr)
}