Задача: Бизнесмен Василий

n = int(input())
a = [int(input()) for _ in range(n)]
for i in range(n-2):
    for j in range(i+1, n-1):
        if sum(a[:i+1]) == sum(a[i+1:j+1]) == sum(a[j+1:]):
            print(a[:i+1], a[i+1:j+1], a[j+1:])

n = int(input())
a = [int(input()) for _ in range(n)]
count = 0
for i in range(n-2):
    for j in range(i+1, n-1):
        count += sum(a[:i+1]) == sum(a[i+1:j+1]) == sum(a[j+1:])
print(count)

from itertools import accumulate
n = int(input())
a = [int(input()) for _ in range(n)]
*pref, = accumulate(a)
count = 0
for i in range(n-2):
    for j in range(i+1, n-1):
        count += pref[i] == pref[j]-pref[i] == pref[n-1]-pref[j]
print(count)

from itertools import accumulate
from bisect import bisect_right as bs
n = int(input())
a = [int(input()) for _ in range(n)]
s = sum(a)
if s%3:
    print(0)
    exit()
*pref, = accumulate(a)
*suff, = accumulate(a[::-1])
pos_pref = [i for i, x in enumerate(pref) if x == s//3]
pos_suff = [n-i-1 for i, x in enumerate(suff) if x == s//3][::-1] # переворачивает т.к. это суффиксы
len_pos_suff = len(pos_suff)
count = 0
for i in pos_pref:
    j = bs(pos_suff, i+1)
    if j < n:
        count += len_pos_suff - j
print(count)

from itertools import accumulate
n = int(input())
a = [int(input()) for _ in range(n)]
s = sum(a)
if s % 3:
    print(0)
    exit()
*pref, = accumulate(a)
*suff, = accumulate(a[::-1])
pos_pref = [int(x == s//3) for i, x in enumerate(pref)]
pos_suff = [int(x == s//3) for i, x in enumerate(suff)]
*count_pos_suff, = accumulate(pos_suff)
count_pos_suff.reverse() # переворачивает т.к. это суффиксы
count = 0
for i, p in enumerate(pos_pref[:-2]):
    if p == 1:
        count += count_pos_suff[i+2]
print(count)