program ciur;
var v:array[2..2000001] of longint;
    i,j,n,c: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 trunc(sqrt(n)) do
  if v[i]=0 then
  for j:=2 to n div i do
    v[i*j]:=1;
  for i:=2 to n do
        if v[i]=0 then
                inc(c);
  writeln(g,C);
   close(g);
  end.