#include<iostream>
#include<vector>
using namespace std;
int N;
vector<int> p, b; // person bike
int cnt(int a, int t) { // person a take t tiers
int temp = min(p[a], b[t]);
p[a] -= temp;
b[t] -= temp;
return temp;
}
int main() {
cin>>N;
p.resize(N+1);
b.resize(N+1);
int total = 0;
for(int i=0; i<N; i++) {cin>>b[i];}
for(int i=0; i<N; i++) {cin>>p[i]; total += p[i];}
int U = 0, D = 0, R = 0;
int ptr = 0;
for(int i=0; i<N; i++) {
while(p[i] && ptr<i) { //還有人，且腳踏車還有>i
U += cnt(i, ptr);
ptr++;
//cout<<i<<" take "<<ptr<<'\n';
}
if(ptr>=N) break;
}
for(int i=0; i<N; i++) {
R += cnt(i, i);
}
D = total - U - R;
cout<<U-D;
}
