#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];
}
int last_nonzero_y = 0;
for (int i = 0; i < n; ++i) {
cin >> y[i];
if (y[i] != 0) {
last_nonzero_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;
for (int i = 1; i < n; ++i) {
int t = min(prex[i - 1] - ans, y[i]);
ans += t;
y[i] -= t;
}
if (prex[last_nonzero_y] > ans) {
y[last_nonzero_y] -= prex[last_nonzero_y] - ans;
y[last_nonzero_y] = max(y[last_nonzero_y], 0LL);
}
for (int i = 0; i < n; ++i) {
ans -= y[i];
}
cout << ans << '\n';
}
