#include<cstdio>
#include<algorithm>
#include<vector>
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);
	printf("%d\n",calcul());
	//for(int i=0; i<n; ++i)
		//printf("%d ",v[i]);
	return 0;
}