#include<algorithm>
#include<fstream>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int v[805],n;
int main()
{
	int st,dr,nr=0,i;
	in>>n;
	for (i=1; i<=n; i++)
		in>>v[i];
	sort(v+1,v+n+1);
	for(int i=1; i<n-1; i++)
	{
		dr=1;
		for(st=i+1; st<n; st++)
		{
			while(v[i]+v[st]>=v[dr] && dr<=n && v[st]<=v[i]+v[dr])
				dr++;
			nr=nr+dr-st-1;
		}
	}
	out<<nr;
	return 0;
}