from bisect import bisect_left

n, m = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

L = [[] for _ in range(n + 1)]
for i in range(m):
    ind = bisect_left(A, B[i])
    L[ind].append(B[i])
ans = 0
for i in range(n + 1):
    if not L[i]:
        continue
    if i == 0:
        ans += A[0] - L[0][0]
    elif i == n:
        ans += L[i][-1] - A[n - 1]
    else:
        if len(L[i]) == 1:
            ans += min(L[i][0] - A[i - 1], A[i] - L[i][0])
        else:
            min_d = 10**10
            min_d = min(min_d, L[i][-1] - A[i - 1])
            min_d = min(min_d, A[i] - L[i][0])
            for j in range(len(L[i]) - 1):
                tmp = L[i][j] - A[i - 1] + A[i] - L[i][j + 1]
                min_d = min(min_d, tmp)
            ans += min_d
print(ans)