#include <bits/stdc++.h>

using namespace std;

using int64 = long long;

int main()
{
  int N, A[100];

  cin >> N;
  for(int i = 0; i < N - 1; i++) {
    cin >> A[i];
  }

  int sum = 0;
  int64 ret = 0;
  for(int i = 0; i < N; i++) {
    int x, y;
    cin >> x >> y;
    sum -= x;
    sum += y;
    ret += 1LL * A[i] * sum;
  }

  cout << ret << endl;
}