n = int(input())
l = list(map(int,input().split()))
l1 = []
l.sort()
r = set()

#存入集合去重
for i in l:
    r.add(i)

#将集合转存入列表
for i in r:
    l1.append(i)
s = 0

for i in range(len(l1)):
    for j in range(i+1,len(l1)):
        for x in range(j+1,len(l1)):
            if l1[i]+l1[j]==l1[x]:
                s += 1
print(s)