#include<iostream>
#include<vector>
using namespace std;
int N,M,A[2<<17],B[2<<17];
main()
{
	cin>>N>>M;
	for(int i=0;i<N;i++)cin>>A[i];
	for(int i=0;i<M;i++)cin>>B[i];
	int id=0;
	int ans=0;
	for(int i=0;i<M;)
	{
		while(id<N&&A[id]<B[i])id++;
		int L=id>0?A[id-1]:-1e9;
		int R=id<N?A[id]:2e9;
		int j=i;
		while(j<M&&B[j]<R)j++;
		if(i+1==j)
		{
			ans+=min(R-B[i],B[i]-L);
		}
		else
		{
			int now=min(R-B[i],B[j-1]-L);
			for(int k=i;k+1<j;k++)
			{
				now=min(now,R-B[k+1]+B[k]-L);
			}
			ans+=now;
		}
		i=j;
	}
	cout<<ans<<endl;
}