#include <bits/stdc++.h>
using namespace std;

int main() {
	int n;
	cin >> n;
	int a[n - 1];
	for (auto &i : a) {
		cin >> i;
	}
	int b[n], c[n];
	for (int i = 0; i < n; i++) {
		cin >> b[i] >> c[i];
	}
	int puni[n]{};
	for (int i = 0; i < n - 1; i++) {
		puni[i + 1] = puni[i] - b[i] + c[i];
	}
	int ans = 0;
	for (int i = 0; i < n - 1; i++) {
		ans += puni[i + 1] * a[i];
	}
	cout << ans << endl;
	return 0;
}