include <bits/stdc++.h>

using namespace std; int a[20005], b[1000];

int main() {

int n, ans = 0, m;
cin >> n;
for (int i = 0; i < n; i++) {
	cin >> b[i];
}
for (int i = 0; i < n; i++) {
	for (int x = i + 1; x < n; x++) {
		if (b[x] != b[i]) {
			m = b[i] + b[x];
			a[m] = 1;
		}
	}
}
for (int j = 0; j < n; j++) {
	if (a[b[j]] == 1) {
		ans++;
	}
}
cout << ans;
return 0;

}