# -*- coding: utf-8 -*-

N,M = map(int, input().split()) # len(D)==M
D = []
for i in range(M):
    D.append(int(input()))

D.sort()

min_dist = 30001
for i in range(M-N+1):
    dist = 0
    if D[i]<=0 and D[i+N-1]<=0:
        dist = abs(D[i])
    elif D[i]>=0 and D[i+N-1]>=0:
        dist = D[i+N-1]
    else:
        left = abs(D[i])
        right = D[i+N-1]
        dist = min(2*left+right, 2*right+left)
    min_dist = min(min_dist, dist)

print(min_dist)