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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;

#ifdef LOCAL
#define debug(var) cerr << (#var) << " = " << (var) << endl;
#else
#define debug(var)
#endif

void init() {
  ios_base::sync_with_stdio(0);
  cin.tie(0); cout.tie(0);
}

const int N = 1e5+23;

int a[N];

void solve() {
  int n, k; scanf("%d%d", &n, &k);
  int zero = -1;
  for (int i = 0; i < n; ++i) {
    scanf("%d", a+i);
    if (a[i] == 0) { // real stupid
      --k; --n; --i;
      continue;
    }
    if (zero == -1 && a[i] > 0) zero = i;
  }
  if (zero == -1) zero = n;
  if (k == 0) {
    printf("0");
    return;
  }
  long long ans = 1e15;
  for (long long cur, cnt, i = 0; i < n; ++i) {
    if (a[i] < 0) {
      cnt = zero-i;
      cur = -a[i];
      if (cnt < k) {
	if (k+i-1 >= n) continue;
	cur += -a[i] + a[k+i-1];
      }
    } else {
      cnt = i-zero+1;
      cur = a[i];
      if (cnt < k) {
	if (i-k+1 < 0) continue;
	cur += a[i] + -a[i-k+1];
      }      
    }
    ans = min(ans, cur);
  }
  printf("%lld", ans);
}

int main() {
  init();
  int t = 1; //scanf("%d", &t);
  while (t--) {
    solve();
  }
  return 0;
}