#include <string>
#include <string>
#include <iostream>
#include <algorithm>
using namespace std;
int n, a[100009], b[100009], c[100009];
int main() {
	cin >> n;
	for (int i = 0; i < n - 1; i++) cin >> a[i];
	long long sum = 0, ret = 0;
	for (int i = 0; i < n - 1; i++) {
		cin >> b[i] >> c[i];
		sum += b[i] - c[i];
		ret += a[i] * sum;
	}
	cout << -ret << endl;
	return 0;
}