var f,g:text;
    n,s,c,i:longint;
    v:array[2..2000000] of byte;

begin
  assign(f,'ciur.in');
  assign(g,'ciur.out');
  reset(f);
  rewrite(g);
  readln(f,n);
  s:=0;
  fillchar(v,sizeof(v),1);
  for i:=2 to n do
    if v[i]=1 then
      begin
        c:=i+i;
        inc(s);
        while c<=n do
          begin
            v[c]:=2;
            inc(c,i);
          end;
      end;
  writeln(g,s);
  close(f);
  close(g);
end.