import std.algorithm, std.container, std.conv, std.math, std.range, std.typecons, std.stdio, std.string;

auto rdsp(){return readln.splitter;}
void pick(R,T)(ref R r,ref T t){t=r.front.to!T;r.popFront;}
void readV(T...)(ref T t){auto r=rdsp;foreach(ref v;t)pick(r,v);}
void readC(T...)(size_t n,ref T t){foreach(ref v;t)v=new typeof(v)(n);foreach(i;0..n){auto r=rdsp;foreach(ref v;t)pick(r,v[i]);}}

void main()
{
  int n; readV(n);
  int[] a; readC(n-1, a);

  auto d = new int[](n);
  foreach (i; 0..n) {
    int b, c; readV(b, c);
    d[i] = (i == 0 ? 0 : d[i-1])+c-b;
  }

  auto ans = 0L;
  foreach (i; 0..n-1) ans += d[i]*a[i];
  writeln(ans);
}