n, m = map(int, input().split())
a = list(map(int, input().split()))
b = list(map(int, input().split()))
a = [(i, 0) for i in a]
b = [(i, 1) for i in b]
l = sorted(a + b)
que = []
INF = 10 ** 18
cur = -INF
ans = 0
for i, c in l:
	if c == 0:
		if not que: cur = i; continue
		if len(que) == 1: ans += min(i - min(que), max(que) - cur); cur = i; que = []; continue
		cost = min(max(que) - cur, i - min(que))
		mal, mir = -INF, que[0]
		for j in range(len(que)):
			mal = que[j]
			mir = que[j + 1] if j + 1 < len(que) else -INF
			cost = min(cost, (mal - cur) + (i - mir))
		ans += cost
		cur = i
		que = []
	else:
		que.append(i)
if que: ans += max(que) - cur; que = []
print(ans)