#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
// #define endl '\n'
#define ld long double
#define pb push_back
#define pf push_front
#define mod 10000007
#define se second
#define fi first
#define all(ls) (ls).begin(),(ls).end()
#define int long long
using namespace std;
using namespace __gnu_pbds;
template<typename type>using ordered_set=tree<type,null_type,less<type>,rb_tree_tag,tree_order_statistics_node_update>;
template<typename type>using ordered_multiset=tree<type,null_type,less_equal<type>,rb_tree_tag,tree_order_statistics_node_update>;
void solve(){
int n,ans=0;
cin>>n;
set<int>pos;
int a[n],b[n];
for(int i=0;i<n;i++){
cin>>a[i];
if(a[i]>0)
pos.insert(i);
}
for(int i=0;i<n;i++)
cin>>b[i];
int i=0;
while(pos.size() and i<n){
auto lb=pos.lower_bound(i);
if(lb!=pos.begin()){
lb--;
int tmp=min(a[*lb],b[i]);
ans+=tmp;
a[*lb]-=tmp;
b[i]-=tmp;
if(a[*lb]==0)
pos.erase(lb);
if(b[i]==0)
i++;
}
else
i++;
}
for(int i=0;i<n;i++)
if(pos.count(i))
ans-=max(0LL,b[i]-a[i]);
else
ans-=b[i];
cout<<ans<<endl;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t=1;
// cin>>t;
for(int i=1;i<=t;i++){
// cout<<"Scenario #"<<i<<":"<<" ";
solve();
}
}
