Help! I need 大佬们的 help.

#include <iostream>
#include <algorithm>
using namespace std;


int a[100005];
int main()
{
	int m,n,i,k;
	long long ans=0;
	cin>>m>>n;
	for(i=0;i<m;i++) cin>>a[i];
	sort(a,a+m);
	for(i=0;i<n;i++)
	{
		cin>>k;
		if(a[lower_bound(a,a+m,k)-a]-k<k-a[lower_bound(a,a+m,k)-a-1]) ans+=a[lower_bound(a,a+m,k)-a]-k;
		else ans+=k-a[lower_bound(a,a+m,k)-a-1];
	}
	cout<<ans;
	return 0;
}