N = int(input()) A = list(map(int, input().split())) B = [0] * (2 * N - 1) for i in range(2 * N - 1): if (A[i + 2] - A[i + 1]) % 3 == 1 and (A[i + 1] - A[i]) % 3 == 1: B[i] = 1 elif (A[i + 2] - A[i + 1]) % 3 == 2 and (A[i + 1] - A[i]) % 3 == 2: B[i] = 2 else: B[i] = 0 if B[0] == 0: print(0) exit() if N & 1: ans = B[0] else: ans = B[2] for i in range(2 * N - 1): if i & 3 == 2: if B[i] != B[2]: print(0) exit() elif i & 3 == 0: if B[i] != B[0]: print(0) exit() else: if B[i] != 0: print(0) exit() print(ans)