代码：

#include<iostream>
using namespace std;
int n, cnt, a[101], flag[101];
int main()
{
	cin >> n;
	for (int i = 1; i <= n; i++) cin >> a[i];
	for (int i = 1; i <= n; i++)
	{
		for (int j = i + 1; j <= n; j++)
		{
			for (int k = 1; k <= n; k++)
			{
				if (i != j && a[i] + a[j] == k && !(flag[k]))
				{
					cnt++;
					flag[k] = 1;
				}
			}
		}
	}
	cout << cnt;
	return 0;
}