#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using ld = long double;

const int INF = (1 << 30) - 1;
const ll INF64 = ((ll)1 << 62) - 1;
const double PI = 3.1415926535897932384626433832795;

const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { -1, 0, 1, 0 };

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	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];
	}

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

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

	cout << ans << endl;
	return 0;
}