#include <iostream>
#include <vector>

void solve() {
    int n;
    std::cin >> n;

    std::vector<int> xs(n - 1);
    for (auto& x : xs) std::cin >> x;

    int ans = 0, k = 0;
    for (auto x : xs) {
        int b, c;
        std::cin >> b >> c;
        k += c - b;
        ans += k * x;
    }

    std::cout << ans << std::endl;
}

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

    solve();

    return 0;
}