#include <fstream>
#include <algorithm>

using namespace std;

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

int n, v[3001], i, a, b, nr=0, mid, st, dr;

int main(){
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i];

    sort(v+1, v+n+1);

    for(i=1;i<n-1;i++)
        for(a=1+i;a<n;a++) {

            st=a+1;
            dr=n;
            while(st<=dr){
                mid=(st+dr)/2;
                if(v[mid]<=v[a]+v[i])
                    st = mid+1;
                else
                    dr=mid-1;
            }
            nr += (dr-a);
        }
    fout<<nr;
}