// #pragma GCC optimize("O3")
// #pragma GCC target("avx2")
#include <bitset>
#include <cassert>
#include <cmath>
#include <functional>
#include <map>
#include <math.h>
#include <algorithm>
#include <iostream>
#include <queue>
#include <set>
#include <vector>
#define ll long long
#define ull unsigned ll
#define ld long double
#define ln "\n"
#define ff first
#define ss second
using namespace std;
const ll inf=2e18;
const ll MOD = 1000000007;
void solve(){
ll n; cin >> n;
vector<ll> x(n), y(n);
for (ll i=0; i<n; i++) cin >> x[i];
for (ll i=0; i<n; i++) cin >> y[i];
ll res=0, l=n;
for (ll i=n-1; i>=0; i--){
l=min(l, i);
while (l>=0 and y[i]){
ll rem = min(y[i], x[l]);
y[i]-=rem;
x[l]-=rem;
if (l<i) res+=rem;
if (!x[l]) l--;
}
}
l=0;
for (ll i=0; i<n; i++){
while (l<n and y[i]){
ll rem = min(y[i], x[l]);
y[i]-=rem;
x[l]-=rem;
if (l>i) res-=rem;
if (!x[l]) l++;
}
}
cout << res << ln;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(nullptr);
ll t=1;
// cin >> t;
while (t--) solve();
}
