var x,n,k,i:longint;  a:array[1..20000000] of byte; f,g:text;
  begin
  assign(f,'ciur.in'); reset(f);
  readln(f,n); close(f);
  for i:=1 to n do
  a[i]:=1;
  a[1]:=0;
  for i:=2 to n do
  if (a[i]=1) then
   begin
    x:=2*i;
    k:=k+1;
    while x<=n do
    begin
    a[x]:=0;
    x:=x+i;
    end;
   end;
  assign(g,'ciur.out'); rewrite(g);
  writeln(g,k); close(g);
  end.