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