#include <bits/stdc++.h>
using namespace std;
#define int long long
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];
}
vector<int> prex(n, 0);
prex[0] = x[0];
for (int i = 1; i < n; ++i) {
prex[i] = prex[i - 1] + x[i];
}
int ans = 0;
int taken = 0;
for (int i = 1; i < n; ++i) {
int s = min(y[i], prex[i - 1] - taken);
ans += s;
y[i] -= s;
taken += s + min(x[i - 1] - s, y[i - 1]);
y[i - 1] -= min(x[i - 1] - s, y[i - 1]);
}
y[n - 1] = 0;
for (int i = 0; i < n; ++i) {
ans -= y[i];
}
cout << ans << '\n';
}
