OII Gasoline Stations

#include <algorithm>
#include <iostream>
#include <vector>

long long solve(std::vector<int> prices, std::vector<int> liters);
int main() {
  int N;
  std::cin >> N;
  std::vector<int> prices(N), liters(N);

  for (int &price : prices) {
    std::cin >> price;
  }

  for (int &liter : liters) {
    std::cin >> liter;
  }

  std::cout << solve(prices, liters);
  return 0;
}

long long solve(std::vector<int> prices, std::vector<int> liters) {
  int min_price = prices.at(0);
  long long expense = 0;

  for (int i = 0; i < prices.size(); i++) {
    min_price = std::min(min_price, prices.at(i));
    expense += min_price * liters.at(i);
  }

  return expense;
}