#include<stdio.h>

int main()
{
	int a = 0;
	int str[9];
	for (int i = 0; i < 9; i++) {
		if (a != 0)
			break;
		scanf("%d", &(str[i]));
		if (str[i] != i + 1)
			a = i + 1;
	}

	if (a == 0)
		a = 10;

	printf("%d\n", a);

	return 0;
}