#include<iostream>

using namespace std;

int main() {

	int n;

	cin >> n;

	int* bus_stop = new int[n-1];
	int ans = 0;
	int *b = new int[n];
	int *c = new int[n];

	for (int i = 0;i < n - 1;i++) {
		cin >> bus_stop[i];
	}
	for (int i = 0;i < n;i++) {
		cin >> b[i] >> c[i];
	}

	int sumc=0, sumb=0;
	for (int i = 0;i < n - 1;i++) {
		sumc += c[i],sumb+=b[i];
		ans += (sumc - sumb)*bus_stop[i];
	}

	cout << ans << endl;


	delete bus_stop;
	delete b;
	delete c;

	return 0;
}