import sys
input = sys.stdin.readline

N, M = map(int, input().split())
A = [-10**18]+list(map(int, input().split()))+[10**18]
B = list(map(int, input().split()))
B.reverse()
ans = 0

for i in range(N+1):
    l = []
    
    while B and A[i]<=B[-1]<=A[i+1]:
        l.append(B.pop())
    
    if len(l)==0:
        continue
    
    v = min(l[-1]-A[i], A[i+1]-l[0])
    
    for j in range(len(l)-1):
        v = min(v, l[j]-A[i]+A[i+1]-l[j+1])
    
    ans += v

print(ans)