#include <bits/stdc++.h> 
 
using namespace std;  
 
typedef long long ll;  
typedef pair<int, int> ii;  
 
const int INF = 1e9;  
const ll LINF = 1e18;  
 
const int N = 5e3 + 5; 
 
int n; 
int a[N];
 
int main() {
	ios::sync_with_stdio(false); 
	cin.tie(nullptr); 	
	cin >> n; 
	for (int i = 1; i <= n; i++) cin >> a[i]; 
 
	sort(a + 1, a + n + 1);   
 
	// a[k] < a[i] + a[j] (i < j < k)
	ll ans = 0;  
	for (int i = 1; i <= n; i++) {
		for (int j = i + 1, k = i + 1; j <= n; j++) {
			// k là vị trí lớn nhất thoả mãn a[k] < a[i] + a[j]
			while (k + 1 <= n && a[k + 1] < a[i] + a[j]) k++; 
			ans += k - j; 
		}
	}
 
	cout << ans << '\n'; 
}

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