#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
#define maxn 888
int a[maxn], n;
int cauta_binar (int st, int dr, int suma)
{
    int m;
    while(st<=dr)
    {
        m = (st+dr)/2;
        if (a[m] <= suma)
            st = m+1;
        else dr = m-1;
    }
    if (a[m+1]<=suma && m<n-1) m++;
    if (a[m] > suma) m--;
    return m;
}
int main()
{
    ifstream f("nrtri.in");
    ofstream g("nrtri.out");
    f>>n;
    for (int i = 0; i < n; i++)
        f>>a[i];
    sort(a, a+n);
    int ans = 0;
    for (int i = 0; i < n-2; i++)
        for (int j = i+1; j< n-1; j++)
        {
            //cout<<a[i]<< ' '<<a[j] << ' '<<a[ cauta_binar(j+1, n, a[i]+a[j])]<<' '<<cauta_binar(j+1, n-1, a[i]+a[j]) - j << endl;
            ans += cauta_binar(j+1, n-1, a[i]+a[j]) - j;
        }
    g<<ans;
}