#include <bits/stdc++.h>
using namespace std;
#define all(v) v.begin(), v.end()
#define dis(x,y) min(abs(x-y),2*n-abs(x-y))
int main()
{
int n;
cin>>n;
int a[n],b[n];
for (int i=0;i<n;i++)
cin>>a[i];
set<pair<int,int>> se;
for (int i=0;i<n;i++)
{
cin>>b[i];
if (b[i]) se.insert({i,b[i]});
}
int ans=0;
for (int i=n-2;i>=0;i--)
{
while (a[i])
{
auto it=se.lower_bound({i+1,0});
if (it==se.end())
break;
pair<int,int> p=*it;
int mn=min(a[i],p.second);
a[i]-=mn,ans+=mn;
se.erase(p);p.second-=mn;
if (p.second)
se.insert(p);
}
}
for (int i=0;i<n;i++)
{
while (a[i] && !se.empty())
{
auto it=se.lower_bound({i,0});
if (it==se.end())
{
pair<int,int> p=*se.begin();
int mn=min(a[i],p.second);
a[i]-=mn,ans-=mn;
se.erase(p);p.second-=mn;
if (p.second) se.insert(p);
}
else
{
pair<int,int> p=*it;
int mn=min(a[i],p.second);
a[i]-=mn;
se.erase(p);p.second-=mn;
if (p.second)
se.insert(p);
}
}
}
cout<<ans<<endl;
return 0;
}
