program prim;
var f,g:text;
    nr,i,n:longint;
function prim(x:longint):boolean;
 var i:longint;
 begin
 if (x=1) or (x=0) then prim:=false
  else begin
   prim:=true;
   i:=2;
   while (i<=x div 2) and (prim) do if x mod i=0 then prim:=false
                                                 else i:=i+1;
   end;
  end;
begin
assign (f,'ciur.in');
reset(f);
assign (g,'ciur.out');
rewrite(g);
read(f,n);
nr:=0;
for i:=2 to n do if prim(i) then nr:=nr+1;
write (g,nr);
close(f);
close(g);
end.