Problem:
Score : 300 points

Problem Statement

There are N candles placed on a number line.
The i-th candle from the left is placed on coordinate x_i.
Here, x_1 < x_2 < ... < x_N holds.

Initially, no candles are burning.
Snuke decides to light K of the N candles.

Now, he is at coordinate 0.
He can move left and right along the line with speed 1.
He can also light a candle when he is at the same position as the candle, in negligible time.

Find the minimum time required to light K candles.

Constraints

1 \leq N \leq 10^5

1 \leq K \leq N

x_i is an integer.

|x_i| \leq 10^8

x_1 < x_2 < ... < x_N

Input

Input is given from Standard Input in the following format:

N K
x_1 x_2 ... x_N

Output

Print the minimum time required to light K candles.

Sample Input 1

5 3
-30 -10 10 20 50

Sample Output 1

40

He should move and light candles as follows:

Move from coordinate 0 to -10.

Light the second candle from the left.

Move from coordinate -10 to 10.

Light the third candle from the left.

Move from coordinate 10 to 20.

Light the fourth candle from the left.

Sample Input 2

3 2
10 20 30

Sample Output 2

20

Sample Input 3

1 1
0

Sample Output 3

0

There may be a candle placed at coordinate 0.

Sample Input 4

8 5
-9 -7 -4 -3 1 2 3 4

Sample Output 4

10

Solution in Python (3.4.3) (judge verdict: Wrong Answer)

import math,string,itertools,fractions,heapq,collections,re,array,bisect,sys,random,time

sys.setrecursionlimit(10**7)
inf=10**20
mod=10**9+7

def LI(): return list(map(int,input().split()))
def I(): return int(input())
def LS(): return input().split()
def S(): return input()

def main():
  n,k=LI()
  l=LI()

  l1=[]
  l2=[]

  for x in l:
    if x==0:
      k-=1
    elif x<0:
      l1.append(x)
    else:
      l2.append(x)

  l1.reverse()

  if k==0:
    print(0)
    exit()
  if len(l1)==0:
    print(l2[k-1])
    exit()
  elif len(l2)==0:
    print(l1[k-1])
    exit()

  l1=[0]+l1
  l2=[0]+l2

  sm=inf
  for i in range(k):
    a=0
    if len(l1)<i+1 or len(l2)<k-i+1:
      pass
    else:
      a-=l1[i]
      a+=l2[k-i]*2
      sm=min(sm,a)

  for i in range(k):
    a=0
    if len(l2)<i+1 or len(l1)<k-i+1:
      pass
    else:
      a+=l2[i]
      a-=l1[k-i]*2
      sm=min(sm,a)

  return sm

print(main())