#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
#define nmax 8005
int main()
{
    int i, j, v[nmax], n, nr=0, st, dr, m, last=0;
    fin>>n;
    for(i=1; i<=n; i++)
        fin>>v[i];
    fin.close();
    sort(v+1, v+1+n);
    for(i=1; i<=n-2; i++)
        for(j=i+1; j<=n-1; j++)
        {
            st=j; dr=n;
            while(st<=dr)
            {
                m=(st+dr)/2;
                if(v[m]>v[i]+v[j])
                    dr=m-1;
                else
                {
                    last=m;
                    st=m+1;
                }
            }
            nr+=last-j;
        }
    fout<<nr<<'\n';
    fout.close();
    return 0;
}