#include <fstream>
#include <algorithm>
using namespace std;
int v[100001];

ifstream cin ("nrtri.in");
ofstream cout ("nrtri.out");
int main()
{
    int n, m, x, c = 0 ;
    cin >> n;
    for (int i = 0; i < n; i++) {
        cin >> v[i];
    }
    
    sort (v , v + n);
    
   for (int i = 0; i < n - 2; i++) 
        for (int j = i + 1; j < n - 1; j++) {
            int s = v[i] + v[j];
            int st = j + 1, dr = n;
            while (st <= dr) {
                int mid = st + (dr - st) / 2;
                if (v[mid] >= s) {
                    c += (dr - mid);
                    break;
                }
                if (v[mid] <= s) 
                    st = mid + 1;
                else dr = mid - 1;
            }
        }
        cout << c;
    
    return 0;
}