type tabel=array[2..2000000]of boolean;
var n,i,j,ciur:longint;
        t:tabel;
begin
 assign(input,'ciur.in');
 reset(input);
 read(n);
 close(input);

 for i:=2 to n do t[i]:=true;

 for i:=2 to n do
  begin
   if t[i]<>false then
                begin
                 ciur:=ciur+1;
                 for j:=2 to n div i do
                 t[i*j]:=false;
                end;
  end;

  assign(output,'ciur.out');
  rewrite(output);
  write(ciur);
  close(output);
end.