n = eval(input())
lst = list(map(int, input().split()))
lst = list(set(lst))
lst.sort()
num = 0
for i in range(n-1, 1, -1):
    for j in range(i-1, 0, -1):
        for k in range(j-1, -1, -1):
            if lst[j]+lst[k] == lst[i]:
                num += 1
                break
            elif lst[j]+lst[k] < lst[i]:
                break
        break
print(num)