Program ciur;
type vec=array[1..2000000] of 0..1;
var p:vec; i,j,nr,n:longint;
    f,g:text;
begin
 assign(f,'ciur.in');
 reset(f);
 readln(f,n);
 close(f);
 assign(g,'ciur.out');
 rewrite(g);
 for i:=2 to n do
  begin
   if p[i]=0
    then
     begin
      nr:=nr+1;
      j:=2*i;
      while j<=n do
        begin
         p[j]:=1;
         j:=j+i;
        end;
     end;
  end;
  writeln(g,nr);
  close(g);
end.