# include <bits/stdc++.h>
using namespace std;
int n,c,a[1000010],b,q;
int main(){
	cin>>n>>c;
	for(int i=1;i<=n;i++)cin>>a[i];
	for(int i=1;i<=n;i++){
		cin>>q;
		b+=max(0,q-a[i]);
	}
	cout<<b*c;
	return 0;
}