#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];
}
vector<int> sufx(n, 0);
sufx[n - 1] = 0;
for (int i = n - 2; i >= 0; --i) {
sufx[i] = sufx[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;
}
int taken = ans;
for (int i = n - 1; i >= 0; --i) {
if (y[i] == 0) {
continue;
}
if (sufx[i] > taken) {
int aval = sufx[i] - taken;
taken += min(aval, y[i]);
y[i] -= min(y[i], aval);
}
}
for (int i = 0; i < n; ++i) {
ans -= y[i];
}
cout << ans << '\n';
}
