import os
import sys
n = int(input())
a = map(int, input().split())
s = [0]
for i in a:
    s.append(s[-1] + i)
t = s[-1] // 3
if t * 3 != s[-1]:
    print(0)
else:
    c0 = 0
    c1 = 0
    ind = []
    for i0 in range(1, len(s)):
        i = s[i0]
        if i == t:
            c0 += 1
            ind.append(i0)
        elif i == s[-1] - t:
            c1 += 1
    if t != 0:
        print(c0 * c1)
    else:
        r = 0
        for i in range(len(ind)):
            for j in range(i + 1, len(ind)):
                if ind[j] == n:
                    continue
                r += 1
            
        print(r)