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]:=true;
  i:=2;
  while i<n do
    begin
      while (not t[i]) and (i<n) do
        i:=i+1;
      for k:=2 to (n div i) do
       t[i*k]:=false;
      i:=i+1;
    end;
for i:=2 to n do
  if t[i] then x:=x+1;
    assign(output,'ciur.out');
  rewrite(output);
  write(x);
  close(output);
END.