var n:integer;
    a:array[1..800]of integer;
    nr,i,j,k,l1,l2:longint;
    f,g:text;

begin
assign(f,'nrtri.in');
reset(f);
readln(f,n);
for i:=1 to n do read(f,a[i]);
for i:=1 to n-2 do begin
   for j:=i+1 to n-1 do begin
     l1:=a[i]+a[j];
     l2:=abs(a[i]-a[j]);
     for k:=j+1 to n do if a[k]>=l2 then if a[k]<=l1 then nr:=nr+1;
   end;
end;
assign(g,'nrtri.out');
rewrite(g);
write(g,nr);
close(g);
end.