#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int v[801],n,S;
int main()
{
    fin>>n;
    for (int i=1;i<=n;i++)
        fin>>v[i];
    sort(v+1,v+n+1);
    for (int i=1;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)/2;
                if (v[mid]>s)
                    dr=mid-1;
                else
                    st=mid+1;
            }
        S=S+dr-j;
        }
    fout<<S;
    return 0;
}