#include <stdio.h>

int main(void)
{
	int b[9];
	int i;

	for (i = 0; i < 9; i++) 
		do {
			scanf("%d", &b[i]);
		} while (b[i] < 1 || b[i] > 10);

	for (i = 0; i < 9; i++) 
		if (b[i] != i + 1)
			break;
	
	printf("%d\n", i + 1);
	
	return 0;
}