// #include <bits/stdc++.h>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <map>
#include <vector>
#include <iomanip>
#include <string>
#include <queue>
#include <set>
#include <deque>
using namespace std;
#define int long long
const int N=3e5+5;
const int M=998244353;
const int LOG = 18;
int n , m , c , t=1 , q=1 , x , y;
vector<int>a(N),b(N),p(N);
void solve()
{
cin >> n;
for (int i=0;i<n;i++){
cin >> a[i];
}
int l=0;
for (int i=0;i<n;i++){
cin >> b[i];
l-=b[i];
}
int c=0;
int r=0;
for (int i=0;i<n;i++){
int u=min(b[i],c);
l+=u*2;
c-=u;
b[i]-=u;
r=min(r,c);
r+=min(b[i],a[i]);
c+=a[i];
r=min(r,c);
}
cout << l+r << endl;
}
signed main()
{
ios::sync_with_stdio(0);//DO NOT USE IN INTERACTIVE
cin.tie(0), cout.tie(0);//DO NOT USE IN INTERACTIVE
cout << fixed<<setprecision(9);
// int t=1;
// cin >> t;
for (int _=1;_<=t;_++){
solve();
q++;
}
}
