[백준] 13305번 주유소

import java.util.*;
public class Main
{
	public static void main(String[] args) {
	    
		Scanner kb = new Scanner(System.in);
		
		int n = kb.nextInt();
		
		int[] distance = new int[n-1];
		int[] cost = new int[n];
		
		
		for(int i=0; i<n-1; i++){
		    distance[i] = kb.nextInt();
		}
		
		for(int i=0; i<n; i++){
		    cost[i] = kb.nextInt();
		}
		
		
		long minCost = cost[0];
		long sum  = 0;
		
		for(int i=0; i<n-1; i++){
		    if (minCost>cost[i]){
		        minCost = cost[i];
		    } 
		    sum += minCost*distance[i];
		}
		
		System.out.println(sum);
	}
}