// No.633 バスの運賃
// https://yukicoder.me/problems/no/633
//

#include <iostream>
#include <vector>
using namespace std;

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

    unsigned int n;
    cin >> n;
    vector<int> fees(n, 0);
    for (auto i = 1; i < n; ++i)
        cin >> fees[i];

    int passenger = 0;
    int total_fee = 0;

    for (auto i = 0; i < n; ++i) {
        total_fee += passenger * fees[i];
        int b, c;
        cin >> b >> c;
        passenger -= b;
        passenger += c;
    }
    cout << total_fee << endl;
}