n = int(input()) a = list(map(int, input().split()))

pre_sum = [0] * (n + 1) for i in range(1, n + 1): pre_sum[i] = pre_sum[i - 1] + a[i - 1]

total = pre_sum[n] if total % 3 != 0: print(0) else: target = total // 3 res = 0 count = 0

for j in range(1, n): 
    if pre_sum[j] == 2 * target:
        res += count
    if pre_sum[j] == target:
        count += 1

print(res)