#include<bits/stdc++.h>
using namespace std;
int ans,n,c,r[1000001],a[1000001];
int main(){
    cin>>n>>c;
	for(int i=1;i<=n;i++)cin>>r[i];
	for(int i=1;i<=n;i++){
		cin>>a[i];
		if(a[i]>r[i])ans+=a[i]-r[i];
	}
	ans*=c;
	cout<<ans;
    return 0;
}