program sieve;
var
  p: array[1..2000000] of byte;
  n,r: longint;

procedure ciur(n:longint);
var i,j: longint;
begin
  p[1]:=1;
  for i:=2 to trunc(sqrt(n)) do
  if p[i]=0 then
  for j:=2 to n div i do
    p[i*j]:=1;
  for i:=2 to n do
   if p[i]=0 then inc(r)
end;

begin
  assign(input,'ciur.in');
  reset(input);
  assign(output,'ciur.out');
  rewrite(output);
  readln(n);
  ciur(n);
  writeln(r);
  close(input);
  close(output);
end.