#include <iostream>
#include <algorithm>
using namespace std;
const int NMAX=801;
int a[NMAX];
int main() {
    int n,nr=0;
    cin>>n;
    for(int i=1;i<=n;i++)
        cin>>a[i];
    sort(a+1, a+n+1);
    for(int i=1;i<=n-1;i++)
        for(int j=i+1;j<=n;j++)
        {
            int st = j, dr = n, poz = j;
            while(st <= dr)
            {
                int m = (st + dr) / 2;
                if(a[m] <= a[i] + a[j])
                {
                    st = m + 1;
                    poz = m;
                }
                else
                    dr = m - 1;
            }
            nr+=poz-j;
        }
    cout<<nr;
    return 0;
}