There are N candles placed on a number line. The i-th candle from the left is placed on coordinate xi. Here, x1<x2<...<xN holds.
Initially, no candles are burning. Snake 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≤N≤105
1≤K≤N
xi is an integer.
|xi|≤108
x1<x2<...<xN
Input
Input is given from Standard Input in the following format:
N K
x1 x2 ...... xN
Output
Print the minimum time required to light K candles.
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.
