program pascal;
var f,g:text;
    i,d,n,nr:longint;
    v:array[2..2000000] of longint;
begin
 assign(f,'ciur.in'); reset(f);
 assign(g,'ciur.out'); rewrite(g);
 read(f,n);
 d:=2;   nr:=0;
 while d<=n do
   begin
    if v[d]<>1 then
       begin
         i:=d;
         while i+d<=n do
           begin
            v[i+d]:=1;
            i:=i+d;
           end;
           nr:=nr+1;
       end;
      d:=d+1;
    end;


  write(g,nr);
 close(f);
 close(g);
end.