#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    int k[n-1];
    int p[n];
    for (int i = 0;i < n-1;i++) {
        cin >> k[i];
    }
    for (int i = 0;i < n;i++) {
        cin >> p[i];
    }
    
    long long min_v = p[0];
    long long cnt = 0;
    for (int i=0;i<n-1;i++) {
        if (min_v > p[i]) 
            min_v = p[i];
        
        cnt += min_v*k[i];
        //cout << min_v << " " << cnt << "\n";
    }
    cout << cnt;
    return 0;
}