def read_data():
    N, M = map(int, input().split())
    Ds = [int(input()) for i in range(M)]
    return N, M, Ds

def solve(N, M, Ds):
    Ds.sort()
    minmove = float('inf')
    for i in range(M - N + 1):
        left = Ds[i]
        right = Ds[i + N - 1]
        if left > 0:
            move = right
        elif right < 0:
            move = -left
        else:
            move = (right - left) + min(right, -left)
        minmove = min(minmove, move)
    return minmove

N, M, Ds = read_data()
print(solve(N, M, Ds))