#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int a[802],i1,i2,i3,i,t,n;
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
		fin>>a[i];
	sort(a+1,a+n+1);
	i1=1;
	i2=2;
	i3=3;
	t=0;
	while(i1<=n-2)
	{
		while(i2<=n-1)
		{
			while((a[i1]+a[i2]>=a[i3])&&(i3<=n))
			{
				t++;
				i3++;
			}
			i2++;
			i3=i2+1;
		}
		i1++;
		i2=i1+1;
		i3=i2+1;
	}
	fout<<t;
    return 0;
}