inp = input() N, K = map(int, (inp.split())) inp = input() positions = list(map(int, inp.split())) positions.sort() steps = 0 mid = int(N / 2) for i in range(1, mid + 1): if mid - i >= 0: steps += positions[mid] - positions[mid - i] - K * i if mid + i < N: steps += positions[mid + i] - positions[mid] - K * i print(abs(steps))