#include <bits/stdc++.h>
#define pb push_back
#define SS ios_base::sync_with_stdio(0);cin.tie(nullptr);cout.tie(nullptr);
#define int long long
#define all(v) v.begin(),v.end()
using namespace std;
const int N = 1e4, inf = 1e9 + 1, mod = 998244353;
void solve(){
int n;
cin >> n;
int x[n + 1], y[n + 1];
for(int i = 1; i <= n; i++){
cin >> x[i];
}
for(int i = 1; i <= n; i++){
cin >> y[i];
}
set<int> st;
int ans = 0;
for(int i = 1; i <= n; i++){
st.insert(i);
}
for(int i = 1; i <= n; i++){
auto it = st.lower_bound(i);
if(it == st.begin()) continue;
it--;
int mn = min(x[*it], y[i]);
x[*it] -= mn;
y[i] -= mn;
ans += mn;
if(x[*it] == 0) st.erase(it);
if(y[i] > 0) i--;
}
for(int i = n; i >= 1; i--){
auto it = st.lower_bound(i);
if(it == st.end()) continue;
int mn = min(x[*it], y[i]);
x[*it] -= mn;
y[i] -= mn;
if(*it != mn) ans -= mn;
if(x[*it] == 0) st.erase(it);
if(y[i] > 0) i++;
}
cout << ans;
}
signed main(){
SS
// freopen("trains.in", "r", stdin);
// freopen("trains.out", "w", stdout);
int t = 1;
// cin >> t;
while(t--){
solve();
}
}
