#include<cstdio>
#include<algorithm>
using namespace std;
int n,v[805],s;
int binar(int s,int d,int val)
{
	if(s<=d)
	{
		int m=(s+d)/2;
		if(v[m]==val)
		{
			while(v[m+1]==val)
				m++;
			return m;
		}
		if(v[m]<val && v[m+1]>val)
			return m;
		if(v[m]>val && v[m-1]<val)
			return m-1;
		if(v[m]>val)
			return binar(s,m-1,val);
		return binar(m+1,d,val);
	}
}
int main()
{
	int i,j;
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	scanf("%d",&n);
	for(i=1;i<=n;i++)
		scanf("%d",&v[i]);
	sort(v+1,v+n+1);
	for(i=1;i<n;i++)
		for(j=i+1;j<n;j++)
			s+=binar(j+1,n,v[i]+v[j])-j;
	printf("%d",s);
	return 0;
}