#include <iostream>
#include <vector>
using namespace std;
#define int long long
signed main() {
int N;
cin >> N;
vector<int> slot(N), person(N);
for (int i = 0; i < N; i++) cin >> slot[i];
for (int i = 0; i < N; i++) cin >> person[i];
int ptr = 0, ans = 0;
for (int i = 0; i < N; i++) {
int need = person[i];
for (int t = ptr; t < i && need; t++) {
int take = min(need, slot[t]);
slot[t] -= take;
need -= take;
ans += take; // upvotes
}
while (ptr < N && slot[ptr] == 0) ptr++; // 修正順序
person[i] = need;
}
// 分配同 tier
for (int i = 0; i < N; i++) {
int take = min(slot[i], person[i]);
slot[i] -= take;
person[i] -= take;
// 同 tier → 不加不扣
}
// 剩下的人只能往更高 tier → downvotes
for (int i = 0; i < N; i++) {
ans -= person[i];
}
cout << ans;
}
