#include<fstream.h>


int poz(int v[802], int p, int u)
	{
	int piv=v[p],aux;
	while (p<u)
		{
		if (v[p]>v[u]) {
			       aux=v[p];
			       v[p]=v[u];
			       v[u]=aux;
			       }
		if (piv==v[p]) u--;
			else p++;
		}
	return p;
	}

void quick (int v[802], int a, int b)
	{
	int k;
	if (a<b) {
		 k=poz(v,a,b);
		 quick(v,a,k-1);
		 quick(v,k+1,b);
		 }
	}

int cautbin(int v[802], int n, int val)
	{
	int p=1,i=0;
	for (;p*2<=n;p*=2);
	for (;p;p/=2)
		if (i+p<=n && v[p+i]<=val) i+=p;
	return i;
	}

int main()
{
int v[802],n,i,j,nr=0;
ifstream f("nrtri.in");
f>>n;
for (i=1;i<=n;i++) f>>v[i]; f.close();
quick(v,1,n);
for (i=1;i<n-1;i++)
	for (j=i+1;j<n;j++)
		nr+=cautbin(v,n,v[i]+v[j])-j;
ofstream g("nrtri.out");
g<<nr;g.close();
return 0;
}