input()
row = input().split(' ')
nums = [int(n) for n in row]
count = 0
for n in nums:
    nums2 = [n for n in nums if n != n]
    stop = False
    for i in range(0,len(nums2)):
        for n2 in nums2[i+1:]:
            if nums2[i] + n2 == n:
                count += 1
                stop = True
                break
        if stop:
            break
print(count)