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

int main() {
    int n; cin >> n;
    vector<int> a(n - 1);
    for (int &ai: a) cin >> ai;
    a.emplace_back(0);
    int num = 0, res = 0;
    for (int i = 0; i < n; i++) {
        int b, c; cin >> b >> c;
        num += -b + c;
        res += num * a[i];
    }
    cout << res << endl;
    return 0;
}