#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;

int main() {
    int n;
    cin >> n;

    vector<int> a(n);
    for (int i = 0; i < n - 1; i++) {
        cin >> a[i];
    }

    int r = 0, s = 0;
    for (int i = 0; i < n; i++) {
        int b, c;
        cin >> b >> c;

        s += c - b;
        r += s * a[i];
    }

    cout << r << endl;

    return 0;
}