"""

"""

import sys
from sys import stdin

N,M = map(int,stdin.readline().split())

A = [-10**10] + list(map(int,stdin.readline().split())) + [10**10]
B = list(map(int,stdin.readline().split()))

B.reverse()

ans = 0
for i in range(N+1):

    al = A[i]
    ar = A[i+1]

    dlis = [al]
    while len(B) > 0 and al <= B[-1] <= ar:
        dlis.append(B[-1])
        del B[-1]

    dlis.append(ar)

    d2 = []
    for j in range(len(dlis)-1):
        d2.append(dlis[j+1]-dlis[j])

    #print (al,ar,d2)
    ma = max(d2)
    ans += sum(d2) - ma

print (ans)