#include<bits/stdc++.h>
using namespace std;
// #define int long long
#define DEBUG 0
#define printf if(DEBUG) printf
constexpr int MAXN = 3e5+10;
signed main() {
ios::sync_with_stdio(false); cin.tie(nullptr);
int n;cin>>n;
vector<int> x(n),y(n);
for(int i = 0; i < n; i++) cin>>x[i];//supply
for(int i = 0; i < n; i++) cin>>y[i];// demand
int score = 0;
stack<pair<int,int>> st; // idx, value of CUSTOMERS.
for(int i = n-1; i >= 0; i--) {
while (x[i] > 0 && !st.empty()) {
auto [j, val] = st.top(); st.pop();
// y[j] is the customer. not the other way round.
// so j is the customer.
int take = min(x[i], y[j]);
x[i] -= take;
y[j] -= take;
score += take;
if (y[j] > 0) {
st.push({j, y[j]});
}
}
if (y[i] > 0) {
st.push({i, y[i]});
}
}
// 2. penalty
for(int i = n-1; i >= 0; i--) {
if (y[i] == 0) continue;
int take = min(y[i], x[i]);
y[i] -= take;
x[i] -= take;
// score += 0 * take.
if (y[i] > 0) {
score -= y[i];
y[i] = 0;
}
}
cout<<score<<endl;
}
