#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int main()
{
    int n;
    fin>>n;
    vector<int>v(n);

    for(int i=0;i<n;i++)
        fin>>v[i];

    sort(v.begin(),v.end());
    int cont=0;

    for(int l1=0;l1<n;l1++){
        for(int l2=l1+1;l2<n;l2++){

            int stg=l2+1;
            int dr=n-1;
            int l3=l2;
            while(stg<=dr){
                int mij=(stg+dr)/2;
                if(v[l1]+v[l2]>=v[mij]){
                    l3=mij;
                    stg=mij+1;
                }
                else{
                    dr=mij-1;
                }
            }
            cont+=l3-l2;
            //cout<<v[l1]<<" "<<v[l2]<<" "<<v[l3]<<endl;

        }
    }

    fout<<cont;

    return 0;
}