from bisect import bisect
N, M = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

C = [[] for _ in range(N+1)]
for i in range(N):
    C[i+1].append(A[i])

for b in B:
    ind = bisect(A, b)
    C[ind].append(b)
for i in range(N):
    C[i].append(A[i])

ans = 0
for i in range(1, N):
    if len(C[i]) == 2:
        continue
    L = C[i][-1]-C[i][0]
    v = L
    for j in range(len(C[i])-1):
        v = min(v, L-(C[i][j+1]-C[i][j]))
    ans += v

if len(C[0]) > 1:
    ans += C[0][-1]-C[0][0]
if len(C[N]) > 1:
    ans += C[N][-1]-C[N][0]

print(ans)