abc135_c - City Savers

using namespace std;
using vi = vector<int>;
using ll = long long;
int main(void)
{
    int n;
    ll cur_killed, total_killed;
    vi a, b;
    cin >> n;
    a.resize(n + 1), b.resize(n);
    for (auto &ai : a)
        cin >> ai;
    for (auto &bi : b)
        cin >> bi;
    total_killed = 0;
    for (int i = 0; i < n; ++i)
    {
        cur_killed = min(b[i], a[i] + a[i + 1]);
        total_killed += cur_killed;
        a[i + 1] -= max(0LL, cur_killed - a[i]);
    }
    cout << total_killed << endl;
    return 0;
}