#include <fstream>
#include <algorithm>

using namespace std;

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

int n,v[801],S;

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

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

    return 0;
}