#include <fstream>
#include <algorithm>

using namespace std;

ifstream cin("nrtri.in");
ofstream cout("nrtri.out");

int n, v[802], tri;

int main()
{
    cin >> n;
    for(int i=1; i<=n; ++i)
        cin >> v[i];

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

    for(int i=1; i<n; ++i)
    {
        for(int j=i+1; j<=n; ++j)
        {
            int st = j+1, dr = n, bun = 0;
            while(st <= dr)
            {
                int mij = (st + dr)/2;
                if(v[mij] <= v[i]+v[j])
                {
                    st = mij +1;
                    bun = mij;
                }else dr = mij - 1;
            }
            if(bun != 0)
                tri = tri + bun - j;
        }
    }
    cout << tri;
    return 0;
}