#include <iostream>
#include <algorithm>
#include <vector>

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 ans = 0;
  int curr = 0;
  for (int i = 0; i < n; i++) {
    int b, c;
    cin >> b >> c;
    curr -= b;
    curr += c;
    ans += curr * a[i];
  }
  cout << ans << endl;
}