代码如下：

#include<cstdio>
using namespace std;

int a[105];
int sum[4995];

int main () {
	int n;
	scanf ("%d", &n);
	for (int i = 1; i <= n; i++) 
		scanf ("%d", &a[i]);
	int tmp = 1;
	for (int i = 1; i < n; i++) {
		for (int j = i + 1; j <= n; j++){
				sum[tmp] = a[i] + a[j];
				tmp++;
		}
	}
	int cnt = 0;
	for (int i = 1; i <= n; i++) {
		for (int j = i; j <= (n * n - n) / 2; j++) {
			if (sum[i] == a[j]) {cnt++; break;}
		}
	}
	printf ("%d", cnt);
	return 0;
}