#include <fstream>
#include <algorithm>
#include <vector>
using namespace std;
vector <int> v;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int main()
{
    int x,n,k,i,s=0,ind;
    fin>>n;
    for(i=1;i<=n;i++)
    {
    	fin>>x;
    	v.push_back(x);
    }
    sort(v.begin(),v.end());
    vector <int>:: iterator it,it1,it2;
    for(it1=v.begin();it1!=v.end()-2;it1++)
    {
    	for(it2=it1+1;it2!=v.end()-1;it2++)
    	{
    		k=(*it1)+(*it2);
    		it=upper_bound(it2+1,v.end(),k);
    		ind=(int)(it-it2-1);
    		s=s+ind;
    	}
    }
    fout<<s;
    return 0;
}