哪里错啦

#include<bits/stdc++.h>
using namespace std;
#define N (int)1e8
int a[N],b[N];
int main(){
	int n,m,i,j,sum=0;
	cin>>n>>m;
	for(i=0;i<n;i++){
		cin>>a[i];
	}
	for(j=0;j<m;j++){
		cin>>b[j];
	}
	sort(a,a+n);
	//int l,r,mid;
	for(i=0;i<m;i++){
		int l=0,r=n;
		while(l<r){
			int mid=(l+r)/2;
			if(a[mid]<=b[i]){
				l=mid+1;
			}
			else{
				r=mid-1;
			}
		}
		if(b[i]<=a[0]){
			sum+=a[0]-b[i];
		}
		else{
			sum+=min(abs(a[l-1]-b[i]),abs(a[l]-b[i]));
		}
	}
	cout<<sum;
	return 0;
}