#include <bits/stdc++.h>
#define pb push_back
#define all(v) (v).begin(),(v).end()
#define ll long long int
using namespace std;
int main() {
ll n, r = 0; cin >> n;
vector<ll> x(n), y(n);
for (int i = 0; i < n; i++) cin >> x[i];
for (int i = 0; i < n; i++) cin >> y[i];
ll cur = n-1;
for (int i = n-1; i >= 0; i--) {
if (cur < 0) continue;
while (y[i] > 0) {
while ((cur >= 0) && (cur >= i || x[cur] == 0)) cur--;
if (cur < 0) break;
if (y[i] <= x[cur]) {
x[cur] -= y[i];
r += y[i];
y[i] = 0;
} else {
y[i] -= x[cur];
r += x[cur];
x[cur] = 0;
}
}
}
ll c = 0;
for (int i = n-1; i >= 0; i--) {
if (c == n) continue;
while (y[i] > 0) {
while (c < n && x[c] == 0) c++;
if (c == n) break;
if (y[i] <= x[c]) {
if (i < c) r -= y[i];
if (i > c) r += y[i];
x[c] -= y[i];
y[i] = 0;
} else {
if (i < c) r -= x[c];
if (i > c) r += x[c];
y[i] -= x[c];
x[c] = 0;
}
}
}
cout << r;
return 0;
}
