#include <iostream>
#include <algorithm>

using namespace std;


int v[1001],n,i,j, st, dr, aux, x, sol, mid;
int main()
{
    cin>>n;
    for(i=1;i<=n;i++)
        cin>>v[i];

    sort (v+1,v+n+1);
    for (i=1;i<=n-2;i++)
        for (j=i+1;j<=n-1;j++)
	{
            x =v[i]+v[j];
            st =j+1;
            dr =n;
            while (st<=dr)
	    {
                mid=(st+dr)/2;
                if (v[mid]<x)
                    st = mid+1;
                else
                    dr = mid-1;
            }
            sol += dr-j;
        }
    cout<<sol;
    return 0;
}