var t:array[1..2000000] of boolean;
    i,n,k,x:longint;

BEGIN
  assign(input,'ciur.in');
  reset(input);
  readln(n);
  x:=0;
  close(input);
  for i:=2 to n do
  t[i]:=false;
  i:=2;
  while i<n do
    begin
      while t[i] and (i<n) do
        i:=i+1;
      for k:=1 to (n div i) do

       t[i*k]:=true;
      x:=x+1;
      i:=i+1;
    end;
  assign(output,'ciur.out');
  rewrite(output);
  write(x-1);
  close(output);
END.