// #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=0;
multiset<pair<ll, ll>> cand;
for (ll i=0; i<n; i++){
// cout << i << ": " << l << ":" << res << ln;
while (l<i and y[i]){
ll rem = min(y[i], x[l]);
y[i]-=rem;
x[l]-=rem;
res+=rem;
if (!x[l]) l++;
}
while (y[i] and !cand.empty()){
auto cur=*cand.begin();
cand.erase(cand.begin());
y[cur.ss]+=cur.ff;
x[cur.ss]+=cur.ff;
ll rem = min(x[cur.ss], y[i]);
x[cur.ss]-=rem;
y[i]-=rem;
res+=rem;
if (x[cur.ss]){
rem = min(x[cur.ss], y[cur.ss]);
x[cur.ss]-=rem;
y[cur.ss]-=rem;
cand.insert({rem, cur.ss});
}
}
if (y[i]){
assert(l==i);
ll rem = min(y[i], x[i]);
y[i]-=rem;
x[i]-=rem;
cand.insert({rem, i});
if (!x[i]) l++;
}
}
// cout << res << ln;
// for (ll i=0; i<n; i++) cout << x[i] << ' ';
// cout << ln;
// for (ll i=0; i<n; i++) cout << y[i] << ' ';
// cout << ln;
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();
}
