#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int nmax = 9000;
const int valmax = 7000;

int fr[2*valmax+5];
int v[nmax+5];
ll frm[2*valmax+5];

int main() {
	ifstream f("medie.in");
	ofstream g("medie.out");

	int n; f >> n;
	for(int i=1; i<=n; i++) {
		f >> v[i];
		fr[v[i]]++;
	}
	ll ans = 0;
	for(int i=1; i<=valmax; i++) {
		ans = ans + 1LL * fr[i] * (fr[i]-1) * (fr[i]-2) / 2;
		for(int j=i+1; j<=valmax; j++) 
			frm[i+j] += 1LL * fr[i] * fr[j];
	}
	cout << fr[1] << "\n";
	for(int i=1; i<=valmax; i++) ans = ans + 1LL * fr[i] * frm[2*i];
	g << ans;
	return 0;
}