#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int n,i,j,v[805],nrPosib;
int CB(int key)
{
    int Left=1,Right=n,Mid=(Left+Right)>>1;
    while (Left<=Right)
    {
        if ((v[Mid]<=key && v[Mid+1]>key) || (v[Mid]<=key && Mid==n)) return Mid;
        else if (v[Mid]<=key && v[Mid+1]<=key) Left=Mid+1;
        else Right=Mid-1;
        Mid=(Left+Right)>>1;
    }
    return 0;
}
int main()
{
    f>>n;
    for (i=1;i<=n;i++) f>>v[i];
    sort(v+1,v+n+1);
    for (i=1;i<n-1;i++)
    {
        for (j=i+1;j<n;j++)
        {
            nrPosib=nrPosib+CB(v[i]+v[j])-j;
        }
    }
    g<<nrPosib;
    return 0;
}