#include "bits/stdc++.h"
using namespace std;
     
#define DEBUG(x) cout<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cout<<#v<<":";for(int i=0;i<v.size();i++) cout<<" "<<v[i]; cout<<endl
     
typedef long long ll;
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll, ll>
const int inf = 1000000001;
const ll INF = 1e18;
#define MOD 1000000007
#define mod 1000000009
#define pi 3.14159265358979323846
#define Sp(p) cout<<setprecision(15)<<fixed<<p<<endl;
int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };

int main() {
  int n, i;
  cin >> n;
  vi a(n);
  for (i = 0; i < n - 1; i++) {
    cin >> a[i];
  }
  vi num(n);
  
  for (i = 0; i < n; i++) {
    int b, c;
    cin >> b >> c;
    num[i] += c - b;
  }
  vi sum(n + 1);
  for (i = 0; i < n; i++) {
    sum[i + 1] = sum[i] + num[i];
  }
  //DEBUG_VEC(sum);
  int ans = 0;
  for (i = 0; i < n; i++) {
    ans += a[i] * (sum[i + 1]);
  }
  cout << ans << endl;
}