#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];
    }
    long long sol = 0;
    sort (v , v + n);
    int r;
   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 - 1;
            int r = j;
            while (st <= dr) {
                int mid = st + (dr - st) / 2;
               if (v[mid] <= s) { 
               r = mid;
               st = mid + 1;
              }  else {
                  dr = mid - 1;  
                }
            }
            sol += (r - j);
        }
        cout << sol;
    
    return 0;
}