var v:array[1..2000000] of boolean;
    i, j, n, c:longint;
    f, g:text;

begin
assign (f, 'ciur.in'); reset (f);
assign (g, 'ciur.out'); rewrite (g);

readln (f, n);
c:=0;
for i := 2 to n do
  begin
  if v[i]=false then
    begin
    c:=c+1;
    j:=i+i;
    while j<=n do
      begin
      v[j] := true;
      j:=j+i;
      end;
    end;
  end;

writeln (g, c);
close (f); close (g);
end.