#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
# define max 1000001
int v[801];

int CautareBinara(int i, int j, int s)
{
    int mij = (i + j)/2;
    if(i > j) return -1;
    if(i == j && v[i] <= s) return mij;
    if(s < v[mij])
        return CautareBinara(i, mij - 1, s);
    if(v[mij+1] <= s)
        return CautareBinara(mij + 1, j, s);
    return mij;
}

int main()
{
    ifstream f("nrtri.in");
    ofstream g("nrtri.out");
    long long int n, i, j, x, nr = 0;
    f>>n;
    for(i = 1; i <= n; i++)
        f >> v[i];
    sort(v + 1, v + n + 1);
    for(i = 1; i <= n - 2; i++)
        for(j = i + 1; j <= n - 1; j++)
        {
            x = CautareBinara(j + 1, n, v[i] + v[j]);
            if(x != -1)
                nr += x - j;
        }
    g<<nr;
    f.close();
    g.close();
    return 0;
}