#include <bits/stdc++.h>
#define ll long long
#define ff first
#define ss second
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define pb push_back
#define ertunt return
#define vodka void
#define sleepearly ertunt
using namespace std;
int main() {
ll n;
cin >> n;
vector<ll> a(n);
for (ll i = 0; i < n; i++) cin >> a[i];
set<ll> s;
vector<ll> b(n);
for(ll i = 0; i < n; i++){
cin >> b[i];
if(b[i] > 0) s.insert(i);
}
ll ans = 0;
for(ll i = 0; i < n; i++){
while(a[i] > 0 && !s.empty()){
auto it = s.upper_bound(i);
if(it == s.end()) break;
ll j = *it;
ll x = min(a[i], b[j]);
ans += x;
a[i] -= x;
b[j] -= x;
if(b[j] == 0) s.erase(it);
}
}
for(ll i = 0; i < n;i++){
ans-=max(0ll,b[i] - a[i]);
}
cout << ans;
}
