#include<bits/stdc++.h>
using namespace std;
using Int = long long;
signed main(){
  Int n;
  cin>>n;
  vector<Int> a(n),b(n),c(n);
  for(Int i=1;i<n;i++) cin>>a[i];
  for(Int i=0;i<n;i++) cin>>b[i]>>c[i];
  Int ans=0,tmp=c[0];
  for(Int i=1;i<n;i++){
    //cout<<i<<":"<<tmp<<endl;
    ans+=a[i]*tmp;
    tmp-=b[i];
    tmp+=c[i];
  }
  cout<<ans<<endl;
  return 0;
}