#include <iostream>
#include <fstream>
#include <algorithm>

#define MAXN 800

using namespace std;

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

int v[MAXN], n;

int bsearch(int x)
{
    int left = 0, right = n - 1, p = -1;

    while(left <= right) {
        int mid = (left + right) / 2;

        if(x >= v[mid])
            p = mid, left = mid + 1;
        else
            right = mid - 1;
    }

    return p;
}

int main(void)
{
    int i, j, result = 0;

    fin >> n;

    for(i = 0; i < n; i++)
        fin >> v[i];

    sort(v, v + n);

    for(i = 0; i < n; i++)
        for(j = i + 1; j < n; j++)
            result += (bsearch(v[i] + v[j]) - j);

    fout << result;

    return 0;
}