n = int(input())
a = list(map(int, input().split()))
d = []
for x, y in zip(a, a[1:]):
    d.append((y - x + 1) % 3 - 1)

m = len(d)
for i in range(0, m, 2):
    if d[i] != d[i + 1]:
        print(0)
        exit(0)
for i in range(0, m - 2, 2):
    if d[i] != -d[i + 2]:
        print(0)
        exit(0)
print(d[m - 1] % 3)