n,m=map(int,input().split())
d=[0]*20001
for i in range(m):
    d[int(input())+10000] += 1
left=0
right=0
acc = 0
for i in range(len(d)):
    acc += d[i]
    right = i
    if acc >= n:
        break

def dist(l, r):
    if r <= 10000:
        return 10000 - l
    if l >= 10000:
        return r - 10000
    return r-l + min(10000 - l, r - 10000)

ans = dist(left, right)
while right < 20000:
    if acc >= n:
        acc -= d[left]
        for i in range(left+1, 20001):
            if d[i] > 0:
                left = i
                break
        else:
            break
        if left >= right:
            acc = d[left]
            right = left
        if acc >= n:
            ans = min(ans, dist(left, right))
            continue

    for i in range(right+1, 20001):
        if d[i] > 0:
            right = i
            break
    else:
        break
    acc += d[right]
    if acc >= n:
        ans = min(ans, dist(left, right))
    
print(ans)