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

l, r = 0, K
A0 = A[0]
plus, minus = sum(a - A0 for a in A[:K]), sum(a - A0 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 * (2 * i - l - r)
    minus += diff * (l + r - N)
    while r < N and (arx := (A[r] - x)) < (alx := (x - A[l])):
        plus += arx - alx
        minus += alx - arx
        r += 1
        l += 1
    ans = min(plus - minus, ans)
print(ans)