#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int n,i,v[805],j,st,dr,s,m,k,nr;
int main()
{
    fin>>n;
    for (i=1;i<=n;i++)
        fin>>v[i];
    sort(v+1,v+n+1);
    for (i=1;i<=n-2;i++)
    {
        for (j=i+1;j<=n-1;j++)
        {
            s=v[i]+v[j];
            st=j+1;
            dr=n;
            while (st<=dr)
            {
                m=(st+dr)/2;
                if (v[m]>=s)
                    dr=m-1;
                else
                    st=m+1;
            }
            for (k=dr;k<=n-1;k++)
                nr++;
        }
    }
    fout<<nr-1;
    return 0;
}