#include<fstream> 
using namespace std; 
ifstream f("nrtri.in"); 
ofstream g("nrtri.out");
void citire(char nume_fis[20],int v[801],int& n)
{int i; 
f>>n; 
for(i=1;i<=n;i++) f>>v[i]; 
}
int main() 
{ 
int n,v[801],nr=0,i,j,k; 
citire("nrtri.in",v,n);
sort(v+1,v+n+1);
for(i=1;i<n-1;i++)
	for(j=i+1;j<n;j++) 
		{k=j+1;
	while(k<=n&&v[j]+v[i]>=v[k]) 
			k++; 
	nr+=k-j-1; 
	i++;}
		g<<nr;
		return 0; 
}