#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <list>
#include <set>
#include <map>
#include <numeric>
#include <regex>
#include <tuple>
#include<iomanip>
using namespace std;

typedef long long ll;
typedef pair<int, int> P;
#define MOD 1000000007 // 10^9 + 7
#define INF 1000000000 // 10^9
#define LLINF 1LL<<60

int a[109];

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

	int N; cin >> N;
	for (int i = 0; i < N-1; i++) cin >> a[i];
	int num = 0;
	ll sum = 0;

	for (int i = 0; i < N; i++) {
		int b, c; cin >> b >> c;
		num += c - b;
		sum += a[i] * num;
	}

	cout << sum << endl;

	return 0;
}