#include <bits/stdc++.h>
using namespace std;
int main() {
cin.tie(nullptr);
ios_base::sync_with_stdio(false);
int n;
cin >> n;
vector<long long> slot; slot.reserve(n);
for (int i = 0; i < n; i++) {
long long x;
cin >> x;
slot.push_back(x);
}
vector<long long> bike; bike.reserve(n);
for (int i = 0; i < n; i++) {
long long x;
cin >> x;
bike.push_back(x);
}
int tierPtr = 0;
int counter = 0;
for (int i = 1; i < n; i++) {
while (bike[i] > 0) {
while (tierPtr < n && slot[tierPtr]==0) {
tierPtr++;
}
if (tierPtr >= i) {
// we don't get a +1 for this
break;
}
if (slot[tierPtr] > bike[i]) {
counter += bike[i];
bike[i] = 0;
slot[tierPtr] -= bike[i];
}
else {
counter += slot[tierPtr];
bike[i] -= slot[tierPtr];
slot[tierPtr] = 0;
}
}
}
int rtierPtr = (n-1);
for (int i = (n-1); i >= 0; i--) {
//can take +0
if (slot[i] > 0) {
if (bike[i] > slot[i]) {
bike[i] -= slot[i];
slot[i] = 0;
}
else {
slot[i] -= bike[i];
bike[i] = 0;
}
}
}
for (int i : bike) {
counter -= i;
}
cout << counter << endl;
return 0;
}
