program porez;
var
  n,i:longint;
  k,s:int64;
  a,sup:array[1..100000] of longint;
  f,g:text;

begin
  assign(f,'porez.in');
  assign(g,'porez.out');
  reset(f);
  rewrite(g);
  readln(f,n,k);
  for i:=1 to n do
    read(f,a[i]);
  for i:=2 to n do
    read(f,sup[i]);
  s:=0;
  for i:=1 to n do
    s:=s+a[i];
  writeln(g,trunc(s/k)+1);
  close(f);
  close(g);
end.
