//EGOI 2024 Bike Parking
//https://qoj.ac/contest/1765/problem/9187
#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using vll = vector<ll>;
int main(){
ll n, ans=0;
cin >> n;
vll A(n), B(n); stack<ll> stk;
for(int i=0; i<n; i++) cin >> A[i];
for(int i=0; i<n; i++) cin >> B[i];
for(int i=0; i<n; i++){
while(B[i]>0 && !stk.empty()){
ll id=stk.top(), x=min(A[id],B[i]); stk.pop();
A[id]-=x; B[i]-=x; ans+=x;
if(A[id]!=0) stk.push(id);
}
if(A[i]!=0) stk.push(i);
}
for(int i=0; i<n; i++){
ll x=min(A[i],B[i]);
A[i]-=x, B[i]-=x;
}
for(int i=0; i<n; i++) ans-=B[i];
cout << ans << "\n";
}
