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