#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int N;
  cin >> N;
  vector<int> A(N - 1);
  for (auto &&e : A) {
    cin >> e;
  }
  int res = 0, cur = 0;
  for (int i = 0; i < N; i++) {
    int b, c;
    cin >> b >> c;
    cur += c;
    cur -= b;
    res += cur * A[i];
  }
  cout << res << '\n';
  return 0;
}