#include <fstream>
#include <algorithm>

using namespace std;

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

const int N = 801;
int v[N], n;

int tri(int x)
{
    int r = 0, pas;
    pas = 1 << 9;
    r = 0;
    while(pas != 0)
    {
        if(r + pas <= n && v[r+pas] <=x)
        {
            r+=pas;
        }
        pas/=2;
    }
    return r;
}

int main()
{
    int rez = 0, k;
    in>>n;
    for(int i = 1; i <= n; i++)
        in>>v[i];
    sort(v + 1, v + n + 1);
    for(int i = 1; i < n; i++)
        for(int j = i+1; j <= n; j++)
        {
            k = tri(v[i] + v[j]);
            if(k > j)
                rez += k-j;
        }
    out<<rez;
    return 0;
}