#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
signed main() {
ios::sync_with_stdio(false);
cin.tie(NULL);
int n;
cin >> n;
vector<ll> x(n);
vector<ll> y(n);
for (int i = 0; i < n; i++) cin >> x[i];
for (int i = 0; i < n; i++) cin >> y[i];
ll plus = 0;
ll minus = 0;
for (int i = 1; i < n; i++) {
for (int j = i - 1; j >= 0 && y[i] > 0; j--) {
ll take = min(y[i], x[j]);
plus += take;
y[i] -= take;
x[j] -= take;
}
}
for (int i = 0; i < n; i++) {
ll take = min(y[i], x[i]);
y[i] -= take;
x[i] -= take;
}
for (int i = 0; i < n; i++) {
minus += y[i];
}
cout << plus - minus << endl;
}