#include <stdio.h>
int main()
{
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	int i,n,a[801],sch,j,t,s=0;
	scanf("%d",&n);
	for (i=1; i<=n; i++)
		scanf("%d",&a[i]);
	do
	{
		sch=0;
		for (i=1; i<=n-1; i++)
			if (a[i]>a[i+1])
			{
				j=a[i];
				a[i]=a[i+1];
				a[i+1]=j;
				sch=1;
			}
	}
	while(sch);
	for (i=1; i<=n-2; i++)
		for (j=i+1; j<=n-1; j++)
			for (t=n; t>=j+1; t--)
				if (a[i]+a[j]>=a[t])
				{
					s+=t-j;
                    break;
				}					
    printf("%d",s);	
	return 0;
}