#include <bits/stdc++.h>
#define pb push_back
#define all(v) (v).begin(),(v).end()
#define ll long long int
#define fi first
#define se second
using namespace std;
int main() {
ll n, r = 0; cin >> n;
multiset<ll> x; vector<ll> y(n), cnt(n);
for (int i = 0; i < n; i++) {
ll xi; cin >> xi;
if (xi != 0) x.insert(i);
cnt[i] = xi;
}
for (int i = 0; i < n; i++) cin >> y[i];
for (int i = 0; i < n; i++) {
while (y[i] > 0) {
auto it = x.lower_bound(i);
if (it == x.begin()) break;
auto val = *prev(it);
if (y[i] < cnt[val]) {
cnt[val] -= y[i];
r += y[i];
y[i] = 0;
} else {
x.erase(x.find(val));
y[i] -= cnt[val];
r += cnt[val];
cnt[val] = 0;
}
}
}
vector<ll> rx(n);
for (auto p : x) {
rx[p] = cnt[p];
}
ll c = 0;
for (int i = n-1; i >= 0; i--) {
if (c == n) continue;
while (y[i] > 0) {
while (c < n && rx[c] == 0) c++;
if (c == n) break;
if (y[i] <= rx[c]) {
if (i < c) r -= y[i];
if (i > c) r += y[i];
rx[c] -= y[i];
y[i] = 0;
} else {
if (i < c) r -= rx[c];
if (i > c) r += rx[c];
y[i] -= rx[c];
rx[c] = 0;
}
}
}
cout << r;
return 0;
}
