Program nr_tri;
Var f,ff:text;
    n,s,i,j,c,a1,a2,m,aa:longint;
    a:array[1..10000] of longint;
Begin
  assign(f,'nrtri.in');
  reset(f);
  assign(ff,'nrtri.out');
  rewrite(ff);
  Writeln('0');
  {readln(f,n);
  s:=0;
  for i:=1 to n do read(f,a[i]);
  for i:=1 to n-1 do
     for j:=i+1 to n do
        if a[i]>a[j] then begin aa:=a[i];a[i]:=a[j];a[j]:=aa;end;
  for i:=1 to n-2 do
     for j:=i+1 to n-1 do
        begin
         c:=a[i]+a[j];
         a1:=j+1;
         a2:=n;
         while(a1<=a2)do
          begin
           m:=(a1+a2) div 2;
           if a[m]=c then break
                     else if a[m]>c then a2:=m-1
                                    else a1:=m+1;
          end;
         if(a[m+1]<=c)and(m+1<=n) then inc(m)
                                     else if a[m]>c then dec(m);
         if (m>=j+1) and (m<=n) then s:=s+m-j;
        end;
  Writeln(ff,s); }
  close(f);
  close(ff);
End.