from collections import deque
N,M = map(int,input().split())
D = sorted([int(input()) for _ in range(M)])
que = deque(D[:N])
def dist(l,r):
    if l==r:
        return abs(l)
    if 0<=l<r:
        return r
    elif l<r<=0:
        return -l
    return r-l+min(-l,r)
ans = dist(que[0],que[-1])
for i in range(1,M-N+1):
    que.popleft()
    que.append(D[i+N-1])
    ans = min(ans,dist(que[0],que[-1]))
print(ans)