#include<fstream>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int v[801],n,i,a,b,c,s=0;
int main(){
	f>>n;
	for(i=1;i<=n;++i)
		f>>v[i];
	sort (v+1,v+1+n);
	for(a=1;a<=n-2;++a)
		for(b=a+1;b<=n-1;++b){
			c=b+1;
			while(v[a]+v[b]>=v[c]&&c<=n)c++;
				s=s+c-(b+1);
		}
					g<<s<<'\n';
				g.close();
				return 0;
}