def F(L, R, B):
    if not B:
        return 0
    BL = [0] + [b - L for b in B]
    BR = [R - b for b in B] + [0]
    return min(l + r for l, r in zip(BL, BR))


inf = 10 ** 18
N, M = map(int, input().split())
A = [-inf] + list(map(int, input().split())) + [inf]
B = list(map(int, input().split())) + [inf + 10]

ans = 0
j = 0
for i in range(N+1):
    L = A[i]
    R = A[i+1]
    blue = []
    while L < B[j] < R:
        blue.append(B[j])
        j += 1
    ans += F(L, R, blue)

print(ans)