#include<stdio.h>
#include<vector>
#include<algorithm>
using namespace std;
int n,nr;
vector <int> a;
vector <int> ::iterator it;
int main()
{
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	scanf("%d",&n);
	for(int i=0;i<n;i++)
	{
		int x;
		scanf("%d",&x);
		a.push_back(x);
	}
	sort(a.begin(),a.end());
	for(int i=0;i<n;i++)
		for(int j=i+1;j<n;j++)
		{
			it=lower_bound(a.begin(),a.end(),a[i]+a[j]);
			if(it==a.end())
				continue;
			if(a[i]+a[j]<*it)
				it--;
			nr+=it-a.begin()-j;
		}
	printf("%d\n",nr);
	return 0;
}