import sys
input = sys.stdin.readline

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

S=[0]
for a in A:
    S.append(S[-1]+a)

plus=K
minus=N-K

def calc(i,j):
    a=A[i]
    ANS=S[i+1]-a*(i+1)
    ANS+=a*(N-i-1)-(S[-1]-S[i+1])

    if j+K-1<=i:
        ANS+=2*(a*K-(S[j+K]-S[j]))
    elif j>=i:
        ANS+=2*(S[j+K]-S[j]-a*K)
    else:
        ANS+=2*(a*(i-j)-(S[i]-S[j]))
        ANS+=2*(S[j+K]-S[i]-a*(j+K-i))

    return ANS

LANS=1<<100
for i in range(N):
    MIN=0
    MAX=N-K

    while MAX>MIN+5:
        mid1=MIN+(MAX-MIN)//3
        mid2=MIN+(MAX-MIN)//3*2

        if calc(i,mid1)<calc(i,mid2):
            MAX=mid2
        else:
            MIN=mid1

    for j in range(MIN,MAX+1):
        LANS=min(LANS,calc(i,j))

print(LANS)