#include <bits/stdc++.h>
using namespace std;
#define int long long
typedef pair<int, int> ii;
signed main() {
int n;
cin >> n;
vector<int> x(n, 0), y(n, 0);
for (int i = 0; i < n; ++i) {
cin >> x[i];
}
for (int i = 0; i < n; ++i) {
cin >> y[i];
}
stack<ii> available_seats;
available_seats.emplace(x[0], 0);
int ans = 0;
for (int i = 1; i < n; ++i) {
while (y[i] > 0 && !available_seats.empty()) {
int t = min(y[i], available_seats.top().first);
y[i] -= t;
ans += t;
available_seats.top().first -= t;
if (available_seats.top().first == 0) {
available_seats.pop();
}
}
available_seats.emplace(x[i], i);
}
vector<int> leftover(n, 0);
while (!available_seats.empty()) {
leftover[available_seats.top().second] = available_seats.top().first;
available_seats.pop();
}
for (int i = 0; i < n; ++i) {
y[i] -= min(y[i], leftover[i]);
ans -= y[i];
}
cout << ans << '\n';
return 0;
}
