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#include <bits/stdc++.h>
using namespace std;
const int N = 110;
/*
由于每个数的范围都在10000以内，因此两个数的和在20000以内，所以可以开一个长度是20000的bool数组，
然后枚举所有数对，将所有计算出的两数之和标记一下。
然后再枚举每个数，利用bool数组判断它是否是某两个数的和。
*/
int n;
int a[N];
bool st[20010];
int main() {
scanf("%d", &n);
for (int i = 0; i < n; i++) scanf("%d", &a[i]);
for (int i = 0; i < n; i++)
for (int j = 0; j < i; j++)
st[a[i] + a[j]] = 1;
int res = 0;
for (int i = 0; i < n; i++) res += st[a[i]];
printf("%d\n", res);
return 0;
}
