#include<bits/stdc++.h>
using namespace std;
int x[300005];
int y[300005];
vector<int>ppl;
vector<int>lvl;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
int n;cin>>n;
for(int i=0;i<n;i++){
cin>>x[i];
}
for(int i=0;i<n;i++){
cin>>y[i];
}
multiset<int>ms;
for(int i=0;i<n;i++)ms.insert(i);
int ans=0;
for(int i=n-1;i>=0;i--){
//cerr<<i<<":\n";
auto it=ms.lower_bound(i+1);
vector<int>del;
while(it!=ms.end()){
int id=*it;
int mn=min(x[i],y[id]);
ans+=mn;
x[i]-=mn;
y[id]-=mn;
//cerr<<"use:"<<mn<<"\n";
if(y[id]==0)del.push_back(id);
if(x[i]==0)break;
it++;
}
for(auto x:del)ms.erase(x);
}
for(int i=0;i<n;i++){
int mn=min(x[i],y[i]);
x[i]-=mn;
y[i]-=mn;
//cerr<<"left:"<<y[i]<<"\n";
ans-=y[i];
}
cout<<ans;
}
