#include <stdio.h>

int main()
{
	int i, N, A[200003];
	scanf("%d", &N);
	for (i = 1; i <= N * 2 + 1; i++) scanf("%d", &(A[i]));

	int B[200003];
	for (i = 1; i <= N * 2 - 1; i++) {
		if (A[i] == A[i+1] || A[i+1] == A[i+2] || A[i+2] == A[i]) B[i] = 0;
		else if (A[i] == (A[i+1] + 1) % 3) B[i] = 2;
		else B[i] = 1;
	}
	
	int ans = -1;
	if (B[1] == 0) ans = 0;
	for (i = 3; i <= N * 2 - 1; i += 2) if (B[i] == 0 || B[i] == B[i-2]) break;
	if (i <= N * 2 - 1) ans = 0;
	else if (ans != 0) ans = B[N*2-1];
	for (i = 2; i <= N * 2 - 2; i += 2) if (B[i] != 0) break;
	if (i <= N * 2 - 2) ans = 0;
	printf("%d\n", ans);
	fflush(stdout);
	return 0;
}