import java.util.Scanner;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;

class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        for(int i=1; i<11; i++) {
            int x = in.nextInt();
            if(i != x) {
                System.out.println(i);
                break;
            }
        }

        in.close();
    }
}