#include <fstream>
#include <algorithm>
using namespace std;
int n, v[802];
int main()
{
    int i, j, s, st, dr, mij, nr=0;
    ifstream in ("nrtri.in");
    ofstream out ("nrtri.out");
    in>>n;
    for(i=1;i<=n;i++)
        in>>v[i];
    sort (v+1, v+n+1);
    for(i=1;i<n-1;i++)
        for(j=i+1;j<n;j++)      ///1 2 3 4 5 6 7 8 9
        {
            s=v[i]+v[j];
            st=j;
            dr=n+1;
            while(dr-st!=1)
            {
                mij=(st+dr)/2;
                if(v[mij]<=s)
                {
                    st=mij;
                    nr++;
                }
                else
                    dr=mij;
            }
        }
    out<<nr;
    in.close();
    out.close();
    return 0;
}