inp = input()
N, K = map(int, (inp.split()))

inp = input()
positions = list(map(int, inp.split()))

positions.sort()

steps = 0

mid = int(N / 2)

if positions[0] - K < -1000000:
    mid = 0
elif positions[N - 1] + K > 1000000:
    mid = N - 1

for i in range(1, N):
    if mid - i >= 0:
        steps += abs(positions[mid] - positions[mid - i] - K * i)
    if mid + i < N:
        steps += abs(positions[mid + i] - positions[mid] - K * i)


print(abs(steps))