#include <assert.h>
#include <stdio.h>
#include <vector>
#include <iostream>
#define MAXN 1000000

using namespace std;

int N, i, risu;
int P[MAXN];
int G[MAXN];

int main() {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

    assert(1 == scanf("%d", &N));
    for (i = 0; i < N; i++) assert(1 == scanf("%d", &P[i]));
    for (i = 0; i < N; i++) assert(1 == scanf("%d", &G[i]));

    for(i=0; i<N; i++){
        if(P[i]<=P[i+1]){
            P[i+1]=P[i];
        }
    }
    for(i=0; i<N; i++){
        risu=risu+(G[i]*P[i]);
    }
    cout<<risu;  // print the result
    return 0;
}