#include <fstream>

using namespace std;

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

int n,i,j,y,nr,a[802];

int main()
{
    fin >> n;
    for (i=1;i<=n;i++)
        fin >> a[i];
    for (i=1;i<=n-2;i++){
        for (j=i+1;j<=n-1;j++){
            for (y=j+1;y<=n;y++){
                if (a[i]+a[j]>=a[y])
                    nr++;
                else
                    break;
            }
        }
    }
    fout << nr;

    return 0;
}