#include <iostream>
#include <vector>
using namespace std;
int main(){
	int n;
	cin >> n;
	vector<int> a(n - 1);
	for (int i = 0; i < n - 1; i++){
		cin >> a[i];
	}
	vector<int> b(n), c(n);
	for (int i = 0; i < n; i++){
		cin >> b[i] >> c[i];
	}
	int ans = 0;
	int sum = 0;
	for (int i = 0; i < n; i++){
		ans += (b[i] - c[i]) * sum;
		if (i < n - 1){
			sum += a[i];
		}
	}
	cout << ans << endl;
}