def f(L,R,x):
    return -g(0,n,x) + 2*g(L,R,x)

def g(i,j,x):
    return h(i,x)*(1 if i <= x else -1) + h(j,x)*(-1 if j <= x else 1)

def h(j,x):
    return a[x]*(x-j) - (s[j]-s[x])

n,k = map(int,input().split())
*a, = map(int,input().split())

s = a + [0]
for i in range(n)[::-1]:
    s[i] += s[i+1]

L = 0
ans = 1<<60
for i in range(n):
    while L+k < n and a[i]-a[L] > a[L+k]-a[i]:
        L += 1
    v = f(L,L+k,i)
    ans = min(v,ans)
print(ans)