import sys
readline = sys.stdin.readline

def monotoneminima(f, N, X):
    midx = [None]*N
    mval = [None]*N
    
    stack = [(0, N, 0, X)]
    while stack:
        u, d, l, r = stack.pop()
        
        m = (u+d)//2
        av = f(m, l)
        ai = l  
        for i in range(l+1, r):
            fv = f(m, i)
            if fv < av:
                ai = i
                av = fv
        midx[m] = ai
        mval[m] = av
        if u != m and m != d:
            stack.append((u, m, l, ai+1))
        if m+1 != d and u != m+1:
            stack.append((m+1, d, ai, r))
    return midx, mval

def calc(i, j):
    return -g(i, N-1) + 2*g(i, j+K-1) - 2*g(i, j-1)
def g(i, j):
    if j == -1:
        return 0
    if i <= j:
        return A[i]*(2*i-j+1) + S[j] - 2*S[i]
    return A[i]*(j+1) - S[j]


N, K = map(int, readline().split())
A = list(map(int, readline().split()))
S = A[:] + [0]
for i in range(1, N):
    S[i] += S[i-1]
    
mi, mv = monotoneminima(calc, N, N-K+1)
print(min(mv))