N, M = map(int, input().split(' '))
D = [int(input()) for i in range(M)]
D.sort()
ans = 1000000000
for i in range(0, len(D) - N):
    t = D[i: i + N]
    ta = 0
    for j in range(len(t)):
        ta = min(abs(t[0]) + abs(t[0] - t[-1]), abs(t[-1]) + abs(t[0] - t[-1]))
        if ta < ans:
            ans = ta

print(ans)