#include <fstream>
#include <algorithm>

using namespace std;
int v[802],i,st,j,dr,sol,n,numar,mij,rez;
int main()
{
    ifstream f("nrtri.in");
    ofstream g("nrtri.out");
    f>>n;
    for(i=1;i<=n;i++)
        f>>v[i];
    sort(v,v+n+1);
    for(i=1;i<n;i++)
        for(j=i+1;j<=n;j++)
        {
            numar=v[i]+v[j];
            for(st=j,dr=n;st<=dr;)
                {
                mij=(st+dr)/2;
                if(v[mij]>numar)
                    dr=mij-1;
                else {st=mij+1;
                    rez=mij;
                      }
                }
            sol=sol+rez-j;
        }
    g<<sol;
}