#include <fstream>

using namespace std;

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

void sortare(int a[],int n)
{
    int i,j,aux;
    for(i=1; i<n; i++)
        for(j=i+1; j<=n; j++)
            if(a[j] < a[i])
            {
                aux=a[i];
                a[i]=a[j];
                a[j]=aux;
            }
}

int a[30001];

int main()
{
    int n,i,nrt=0,j,k;

    in>>n;
    for(i=1; i<=n; i++)
        in>>a[i];

    sortare(a,n);

    for(i=1; i<=n; i++)
    {
        k = i + 2;
        for(j=i+1; j<=n; j++)
        {

            while(k <= n && a[k] <= a[i] + a[j])
                k++;
                    //out<<a[i]<<" "<<a[j]<<" "<<a[k]<<"\n";
            nrt += k - j - 1;
        }
    }

    out<<nrt;


    return 0;
}