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

using ll = long long;
#define rep(i, n) for(int i = 0; i < n; i++)

int main() {
	int N;
	cin >> N;
	vector<int> a(N - 1);
	rep(i, N - 1) cin >> a[i];
	vector<ll> d(N);
	rep(i, N) {
		int b, c;
		cin >> b >> c;
		d[i] -= b;
		d[i] += c;
	}
	rep(i, N - 1) d[i + 1] += d[i];
	ll ans = 0;
	rep(i, N - 1) ans += a[i] * d[i];
	cout << ans << endl;
}