from bisect import *

def f(L):
    if L == []:
        return 0
    n = len(L)
    ind = bisect_right(A, L[0])
    pre = A[ind - 1]
    nex = A[ind]
    minv = min(nex - L[0], L[-1] - pre)
    for i in range(n - 1):
        val = L[i] - pre + nex - L[i + 1]
        minv = min(minv, val)
    return minv

N, M = map(int, input().split())
inf = 10 ** 18
A = [-inf] + list(map(int, input().split())) + [inf]
B = list(map(int, input().split()))
D = []
for a in A:
    D.append((a, 1))
for b in B:
    D.append((b, 0))
D.sort()

lst = []
ans = 0
for v, flag in D:
    if flag:
        ans += f(lst)
        lst = []
    else:
        lst.append(v)

print(ans)