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

using namespace std;

vector<int>v;
int n;

void citire()
{
	int x,i;
	scanf("%d",&n);
	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;++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",calcul());
	
	return 0;
}