var p : array[0..2000001] of byte;
    i,rez,j,n,n1 : longint;
    f,g : text;
begin
  assign(f,'ciur.in');reset(f);
  assign(g,'ciur.out');rewrite(g);
  read(f,n);
  n1:=trunc(sqrt(n));
    for i:=2 to n1 do
      if p[i]=0 then
      begin
        j:=i*i;
          while j<=n do
          begin
            p[j]:=1;inc(j,i);
          end;
      end;
    for i:=2 to n-1 do
      if p[i]=0 then inc(rez);
  writeln(g,rez);
  close(g);
end.