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

int v[1001];

int main()
{
    ifstream cin("nrtri.in");
    ofstream cout("nrtri.out");

int n,nr=0,i,j,k;
cin>>n;
for(i=1;i<=n;++i)
    cin>>v[i];
sort(v+1,v+n+1);
for(i=3;i<=n;++i)
{
    j=1;
    k=i-1;
    while(j<k)
    {
        while((j<k) and (v[j]+v[k]<v[i]))
            ++j;
        nr=nr+(k-j);
        --k;
    }
}

cout<<nr<<'\n';

    return 0;
}