import sys
from collections import deque
input = lambda :sys.stdin.readline().rstrip()
mi = lambda :map(int,input().split())
li = lambda :list(mi())

n,m = mi()
a = deque(li())
x = []
for b in li():
    while a and a[0]<b:
        x.append(a.popleft())
    x.append(-b)
x += list(a)

ans = abs(x[-1]) - abs(x[0])
pre = -1
mac = 0;
for i in range(n+m):
    if i:
        mac = max(mac, abs(x[i]) - abs(x[i - 1]))
    if x[i] > 0:
        if pre != -1:
            ans -= mac
        pre = i
        mac = 0

print(ans)