#include <bits/stdc++.h>
#define int long long
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
using namespace std;
int N,M,Q;
vector<int> X,y;
struct node {
node* left, *right;
int sum, lazy;
node(){
left=NULL;
left=NULL;
sum=0;
lazy=-1;
}
void update(){
sum=left->sum+right->sum;
}
void propagate(){
if(lazy>-1){
sum=lazy;
if(left!=NULL){
left->lazy=lazy;
right->lazy=lazy;
}
lazy=-1;
}
}
};
void build(node* x, int l, int r){
if(l==r) x->sum=X[l];
else{
x->left=new node();
x->right=new node();
int mid=(l+r)/2;
build(x->left, l, mid);
build(x->right, mid+1, r);
x->update();
}
}
void update(node* x, int l, int r, int qL, int qR, int v){
x->propagate();
if(r<qR||l>qL) return;
if(r<=qR&&l>=qL){
x->lazy=v;
x->propagate();
return;
}
int mid=(l+r)/2;
update(x->left, l, mid, qL, qR,v);
update(x->right, mid+1, r, qL, qR,v);
x->update();
}
int query(node* x, int l, int r, int qL, int qR){
if(r<qL||l>qR) return 0;
x->propagate();
if(r<=qR&&l>=qL){
return x->sum;
}
int mid=(l+r)/2;
return query(x->left, l, mid, qL, qR)+query(x->right, mid+1, r, qL, qR);
}
signed main() {
ios_base::sync_with_stdio(false); cin.tie(nullptr);
cin >> N;
X.resize(N),y.resize(N);
vector<int> Y(N);
for (int i = 0; i < N; i++) cin >> X[i];
for (int i = 0; i < N; i++) cin >> y[i];
for (int i = 0; i < N; i++) Y[i]=y[i];
node* root = new node();
build(root,0,N-1);
int sm=0;
vector<int> kp(N,0);
/*for (int i = 0; i < N; i++)
{
int xsm=sm;
if(y[i]==0||i==0) {kp[i]+=y[i]; continue;}
int l=0, r=i-1;
while(l<r){
int mid=(l+r+1)/2;
int q=query(root,0,N-1,mid,i-1);
if(q>=y[i]){
l=mid;
}else{
r=mid-1;
}
}
if(l+1<i) {
int q=query(root,0,N-1,l+1,i-1);
y[i]-=q;
sm+=q;
update(root,0,N-1,l+1,i-1,0);
}
int q=query(root,0,N-1,l,l);
int df=min(q,y[i]);
sm+=df;
y[i]-=df;
update(root,0,N-1,l,l,q-df);
kp[i]+=y[i];
cout<< "MADE " << sm-xsm << "\n";
for (int j = 0; j < N; j++)
{
cout<< query(root,0,N-1,j,j) << " ";
}
cout<<"\n";
kp[i]=0;
}
cout << "\n";*/
sm=0;
for (int i = 0; i < N; i++)
{
int xsm=sm;
int l=i-1;
while(l>=0){
int df=min(Y[i],X[l]);
X[l]-=df;
Y[i]-=df;
sm+=df;
if(Y[i]==0) break;
l--;
}
kp[i]+=Y[i];
//cout<< "MADE " << sm-xsm << "\n";
for (int j = 0; j < N; j++)
{
//cout<< X[j] << " ";
}
//cout<<"\n";
}
for (int i = 0; i < N; i++){
int df=min(X[i],kp[i]);
kp[i]-=df;
sm-=kp[i];
}
cout << sm << "\n";
return 0;
}
