#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

const int N=1<<10;

int n;
vector <int> v;

void citire()
{
	int x;
	scanf("%d",&n);
	for (int i=1;i<=n;i++)
	{
		scanf("%d",&x);
		v.push_back(x);
	}
}

int calcul()
{
	int i,j,k,nr=0;
	for (i=0;i<n-2;++i)
	{
		for (j=i+1,k=i+2;j<n-1;++j)
		{
			while (k<n && v[i]+v[j]>=v[k])
				++k;
			nr+=k-j-1;
		}
	}
	return nr;
}

int main()
{
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	citire();
	sort(v.begin(),v.begin()+n); // sorteaza vectorul v
	printf("%d",calcul());
	return 0;
}