#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define llong long long

int main() {
    int n;
    cin >> n;
    vector<int> fares(n-1);
    rep(i, n-1) cin >> fares[i];
    int people = 0;
    int result = 0;
    rep(i, n) {
        if(i>0) result += fares[i-1] * people;
        int b, c;
        cin >> b >> c;
        people -= b;
        people += c;
    }

    cout << result << "\n";
}