#include<fstream>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int a[801];
int main()
{
    int aux,i,n,j,b,k=0,pas;
    in>>n;
    for(i=1;i<=n;i++)
        in>>a[i];
    for(i=1;i<=n-1;i++)
        for(j=1;j<i;j++)
        {
            if(a[j]>a[j+1])
            {
                aux=a[j];
                a[j]=a[j+1];
                a[j+1]=aux;
            }
        }
    /*
    for(i=1;i<=n;i++)
        out<<a[i]<<" ";
    */
    for(i=1;i<=n-2;i++)
    {
        for(j=i+1;j<=n-1;j++)
        {
            pas=1<<9;
            b=0;
            while(pas>0)
            {
                if(b + pas <= n && a[i]+a[j]>=a[pas+b] )
                    b+=pas;
                pas/=2;
            }
            if (b >= j)
                k=k+b-j;
        }
    }
    out<<k;
}