from bisect import bisect_left
m, n = map(int, input().split())
b = list(map(int, input().split()))
a = list(map(int, input().split()))
c = a + b
c.sort()
ans = max(c) - min(c) + 1 - m
for i in range(m - 1):
    l = bisect_left(c, b[i])
    r = bisect_left(c, b[i + 1])
    res = 0
    for j in range(l, r):
        res = max(res, c[j + 1] - c[j] - 1)
    ans -= res
print(ans)