from sys import stdin
n, m = [int(x) for x in stdin.readline().rstrip().split()]
a = [int(x) for x in stdin.readline().rstrip().split()]
b = [int(x) for x in stdin.readline().rstrip().split()]

ab = []
for x in a:
    ab.append((x,0))
for x in b:
    ab.append((x,1))

ab.append((-10**10,0))
ab.append((10**10,0))
ab.sort()

ans = 2*10**10 - 1 - n

l = len(ab)
rangemax = 0
for i in range(1,l):
    rangemax = max(rangemax,ab[i][0]-ab[i-1][0])
    if ab[i][1] == 0:
        ans -= rangemax - 1
        rangemax = 0

print("{}".format(ans))