import sys
#input = sys.stdin.readline #文字列につけてはダメ
input = sys.stdin.buffer.readline #文字列につけてはダメ
#sys.setrecursionlimit(1000000)
#import bisect
#import itertools
#import random
#from heapq import heapify, heappop, heappush
#from collections import defaultdict
#from collections import deque
#import copy

def main():
    N,M = map(int,input().split()); INF = pow(10,18)
    A = [-INF] + list(map(int,input().split())) + [INF]
    B = list(map(int,input().split()))
    ans = 0
    j = 0
    for i in range(N+1):
        if j >= M: break
        temp = []
        left,right = A[i:i+2]
        while j < M and B[j] < right:
            temp.append(B[j])
            j += 1
        #print(temp,left,right)
        L = [0]; R = [0]
        for k in range(len(temp)):
            L.append(temp[k] - left)
            R.append(right - temp[-1-k])
        R.reverse()
        #print(L,R)
        mn = INF
        for p,q in zip(L,R):
            mn = min(mn, p+q)
        ans += mn
    print(ans)


if __name__ == '__main__':
    main()