#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; }