var a:array[1..2000005] of boolean;
    n,i,j,p:longint;
    f:text;

begin

assign(f,'ciur.in');
reset(f);
read(f,n);
close(f);

a[1] := false;
for i := 2 to n do
 a[i] := true;

p := 0;
for i := 2 to n do
 if (a[i] = true) then begin
  p := p + 1;
  j := i + i;
  while (j<=n) do begin
   a[j] := false;
   j := j + i;
  end;
 end;

assign(f,'ciur.out');
rewrite(f);
write(f,p);
close(f);

end.