#include <bits/stdc++.h>
using namespace std;

#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define repi(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define all(x) (x).begin(),(x).end()
#define foreach(u,v) for(auto (u) : (v))
#define pb push_back
#define mp make_pair
#define mt make_tuple

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<ll, ll> pll;
typedef vector<ll> vl;

const int inf = 1e9;
const ll linf = 1LL<<60;
const ll mod = 1e9 + 7;
const double eps = 1e-9;

/*
*/

int main()
{
  int n;
  cin >> n;

  vi a(n-1);
  rep(i, n-1) cin >> a[i];

  vi s(n);
  rep(i, n){
    int b, c;
    cin >> b >> c;
    s[i] += c-b; 
    if(i > 0) s[i] += s[i-1];
  }

  int ans = 0;
  rep(i, n-1){
//    cout << s[i] << " ";
    ans += a[i]*s[i];
  }
//  cout << endl;

  cout << ans << endl;

  return 0;
}