#include <fstream>
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

int main(){
	ifstream fin("nrtri.in");
	int n,r=0;
	fin>>n;
	vector<int> V(n);
	for(int i=0;i<n;++i)
		fin>>V[i];
	sort(V.begin(),V.end());
	for(vector<int>::iterator I=V.begin();I+2<V.end();++I)
		for(vector<int>::iterator J=I+1;J+1<V.end();++J){
			vector<int>::iterator K=lower_bound(J+1,V.end(),*I+*J+1);
		//	cout<<*I<<" "<<*J<<" "<<*K<<endl;
			r+=K-1-J;
		}
	ofstream fout("nrtri.out");
	fout<<r<<endl;
	return 0;
}