#include <fstream>
#include <algorithm>

using namespace std;

int v[810];
int n, i, sol, j, k, st, dr, mid;

int main () {
    ifstream fin ("nrtri.in");
    ofstream fout("nrtri.out");

    fin>>n;
    for (i=1;i<=n;i++)
        fin>>v[i];

    sort(v+1, v+n+1);

    for (i=1;i<=n-2;i++)
        for (j=i+1;j<=n-1;j++) {
            st = j+1;
            dr = n;
            while (st <= dr) {
                int mid = (st + dr)/2;
                if (v[mid] > v[i]+v[j])
                    dr = mid - 1;
                else
                    st = mid + 1;
            }
            sol += dr-j;
        }

    fout<<sol;
    return 0;
}