import java.io.InputStream; import java.io.PrintWriter; import java.lang.reflect.Array; import java.math.BigDecimal; import java.util.ArrayDeque; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.HashMap; import java.util.HashSet; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.Map.Entry; import java.util.PriorityQueue; import java.util.Queue; import java.util.Scanner; import java.util.Set; import java.util.Stack; import java.util.TreeMap; import java.util.TreeSet; import static java.util.Comparator.*; public class Main { public static void main(String[] args) { PrintWriter out = new PrintWriter(System.out); Solver solver = new Solver(System.in, out); solver.solve(); out.close(); } } class Solver { Scanner sc; PrintWriter out; public Solver(InputStream in, PrintWriter out) { sc = new Scanner(in); this.out = out; } // ================================================================== public void solve() { int N = Integer.parseInt(sc.next()); int[] A = new int[N]; for (int i = 0; i < N-1; i++) { A[i] = Integer.parseInt(sc.next()); } int ans = 0, b, c, x = 0; for (int i = 0; i < N; i++) { b = Integer.parseInt(sc.next()); c = Integer.parseInt(sc.next()); x += (-b + c); ans += A[i] * x; } out.println(ans); } }