K, N = map(int, input().split())
A = sorted([int(input()) for i in range(N)])
ans = 10**18

for i in range(K - 1, N):
    L, R = A[i - K + 1], A[i]
    if L * R >= 0:
        ans = min(ans, max(abs(L), abs(R)))
    else:
        ans = min(ans, min(abs(L), abs(R)) * 2 + max(abs(L), abs(R)))

print(ans)