#include <bits/stdc++.h>

using namespace std;

void fast_io() {
	ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
}

int main() {
	fast_io();
	int n;
	cin >> n;
	vector<int> a(n);
	map<int, int> cnt;
	for (int i = 0; i < n; i++) {
		cin >> a[i];
		cnt[a[i]]++;
	}
	vector<int> nums;
	vector<long long> cnts{0};
	for (auto [num, count] : cnt) {
		nums.push_back(num);
		cnts.push_back(count + cnts.back());
	}
	long long ans = 0;
	for (int i : nums) {
		if (cnt[i] < 2) {
			continue;
		}
		auto it = lower_bound(nums.begin(), nums.end(), i + i);
		long long res = cnts[it - nums.begin()] - cnt[i];
		ans += res * cnt[i] * (cnt[i] - 1) / 2;
	}
	cout << ans << "\n";
}