백준 13305

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

class Main13305 {

   public static void main(String[] args) throws Exception {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

      int N = Integer.parseInt(br.readLine());

      StringTokenizer st = new StringTokenizer(br.readLine());

      int[] distance = new int[N];
      for (int i = 1; i < N; i++) {
         distance[i] = Integer.parseInt(st.nextToken());
      }

      st = new StringTokenizer(br.readLine());
      int[] fee = new int[N + 1];
      for (int i = 1; i <= N; i++) {
         fee[i] = Integer.parseInt(st.nextToken());
      }

      long answer = 0;
      int min = Integer.MAX_VALUE;
      for (int i = 1; i < N; i++) {
         min = Math.min(min, fee[i]);
         answer += (long)min * distance[i];
      }

      System.out.println(answer);
   }
}