N, M = map(int, input().split())
D = [int(input()) for _ in range(M)]
D.sort()
ans = 3 * 10 ** 4
for i in range(M - N + 1):
    d0 = D[i]
    dn = D[i + N - 1]
    if d0 * dn < 0:
        ans = min(ans, -d0 * 2 + dn, -d0 + 2 * dn)
    else:
        ans = min(ans, max(abs(d0), abs(dn)))
    #print(i,d0,dn)
print(ans)