from heapq import *
from atcoder.dsu import DSU

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)