import numpy as np
n = int(input())
K = input().split(' ')
K.sort()       #从小到大排序
L = np.zeros(n,dtype='int')
flag = np.zeros(n,dtype='int')
for i in range(n):
    L[i] = int(K[i])
for i in range(n-2):
    for j in range(i+1,n-1):
        for g in range(j+1,n):
            if L[i]+L[j]==L[g]:    #找到
                flag[g] = 1
                break
            elif L[i]+L[j]<L[g]:  #后面不会再有了
                break
print(flag.sum())