#include<vector>
#include<algorithm>
#include<cstdio>
using namespace std;
const int N=1<<10;
int n;
vector <int> v;
void citire()
{
	int i,x;
	for(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);
	scanf("%d",&n);
	citire();
	sort(v.begin(),v.end());
	printf("%d",calcul());
	return 0;
}