#include <fstream>
#include <algorithm>

using namespace std;

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

int const N=801;
int const L=9;
int n,v[N],cnt;

int main()
{
    int r,pas=1<<L;
    in>>n;
    for(int i=1; i<=n; i++) in>>v[i];
    sort(v+1, v+n+1);
    for(int i=1; i<n-1; i++)
        for(int j=i+1; j<n; j++)
        {
            r=j;
            pas = 1 << L;
            while(pas!=0)
            {
                if(r+pas<=n && v[r+pas]<=v[i]+v[j])
                {
                    r+=pas;
                }
                pas/=2;
            }
            //out << i << "," << j << " -> " << r << "\n";
            cnt=cnt+r-j;
        }
    out<<cnt;
    return 0;
}