[백준] No.1461 도서관 完

# ---------- Import ----------
import sys
input = sys.stdin.readline

# ---------- Main ----------
positive = []
negative = []

length, limit = map(int, input().split())
books = list(map(int, input().split()))

for v in books:
    if v > 0: positive.append(v)
    else: negative.append(-v)
    
positive = sorted(positive, reverse=True)[::limit]
negative = sorted(negative, reverse=True)[::limit]

if not positive: MAX = negative[0]
elif not negative: MAX = positive[0]
else: MAX = max(positive[0], negative[0])

print(2 * (sum(positive) + sum(negative)) - MAX)