n, k = map(int, input().split())
l = [*map(int, input().split())]
plus = []
minus = []
for i in l:
if i > 0:
plus.append(i)
else:
minus.append(i)
plus.sort(reverse=True)
minus.sort()
distances = []
for i in range(0, len(plus), k):
distances.append(plus[i])
for j in range(0, len(minus), k):
distances.append(-minus[j])
distances.sort()
s = 0
for i in distances[:-1]:
s += i * 2
s += distances[-1]
print(s)