gasoline.cpp

#include <iostream>
#include <fstream>

using namespace std;

int main() {
//  uncomment the following lines if you want to read/write from files
//  ifstream cin("input.txt");
//  ofstream cout("output.txt");

	long long N;
	cin >> N;
	
	int P[N], G[N];
	for (long long i=0; i<N; i++) {
		cin >> P[i];
	}
	for (long long i=0; i<N; i++) {
		cin >> G[i];
	}
	// insert your code here
	long long litres, temp, ans=0;
	
	for (long long i=0; i<N; i++) {
		litres=G[i];
		temp = P[i];
		if (i != N-1) {
			while (temp < P[i+1]) {
				if (i != N-1) {
					i ++;
				} else {
					break;
				}
				litres += G[i];
			}
			ans += temp * litres;
		} else {
			ans += temp * G[i];
		}
	}

	cout << ans << endl;  // print the result
	return 0;
}