import typing


class DSU:
    '''
    Implement (union by size) + (path halving)

    Reference:
    Zvi Galil and Giuseppe F. Italiano,
    Data structures and algorithms for disjoint set union problems
    '''

    def __init__(self, n: int = 0) -> None:
        self._n = n
        self.parent_or_size = [-1] * n

    def merge(self, a: int, b: int) -> int:
        assert 0 <= a < self._n
        assert 0 <= b < self._n

        x = self.leader(a)
        y = self.leader(b)

        if x == y:
            return x

        if -self.parent_or_size[x] < -self.parent_or_size[y]:
            x, y = y, x

        self.parent_or_size[x] += self.parent_or_size[y]
        self.parent_or_size[y] = x

        return x

    def same(self, a: int, b: int) -> bool:
        assert 0 <= a < self._n
        assert 0 <= b < self._n

        return self.leader(a) == self.leader(b)

    def leader(self, a: int) -> int:
        assert 0 <= a < self._n

        parent = self.parent_or_size[a]
        while parent >= 0:
            if self.parent_or_size[parent] < 0:
                return parent
            self.parent_or_size[a], a, parent = (
                self.parent_or_size[parent],
                self.parent_or_size[parent],
                self.parent_or_size[self.parent_or_size[parent]]
            )

        return a

    def size(self, a: int) -> int:
        assert 0 <= a < self._n

        return -self.parent_or_size[self.leader(a)]

    def groups(self) -> typing.List[typing.List[int]]:
        leader_buf = [self.leader(i) for i in range(self._n)]

        result: typing.List[typing.List[int]] = [[] for _ in range(self._n)]
        for i in range(self._n):
            result[leader_buf[i]].append(i)

        return list(filter(lambda r: r, result))

from heapq import *

N, M = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
dsu = DSU(N + M + 1)
X = []
for i, a in enumerate(A, start=1):
    X.append((a, i, 0))
    dsu.merge(0, i)
for i, b in enumerate(B, start= N + 1):
    X.append((b, i, 1))
X.sort()
Q = []
for i in range(1, N + M):
    a0, b0, c0 = X[i]
    a1, b1, c1 = X[i - 1]
    if c0 == 1 or c1 == 1:
        heappush(Q, (a0 - a1, b0, b1))
ans = 0
while Q:
    a, b, c = heappop(Q)
    if dsu.same(b, c):
        continue
    ans += a
    dsu.merge(b, c)
print(ans)