N, K = map(int, input().split())
A = tuple(map(int, input().split()))

l, r = 0, K
plus, minus = sum(a - A[0] for a in A[:K]), sum(a - A[0] for a in A[K:])
ans = plus - minus
for i in range(1, N):
    x = A[i]
    diff = A[i] - A[i - 1]
    plus -= diff * (r - i)
    plus += diff * (i - l)
    minus -= diff * (N - r)
    minus += diff * l
    while r < N and A[r] - x < x - A[l]:
        plus += A[r] - x
        minus -= A[r] - x
        r += 1

        plus -= x - A[l]
        minus += x - A[l]
        l += 1
    ans = min(plus - minus, ans)
print(ans)