#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];
ll j = 0;
set<ll>s;
ll b[n];
for(ll i = 0; i < n; i++){
cin >> b[i];
if(b[i] > 0){
s.insert(i);
j+=b[i];
}
}
ll ans = 0;
ll k = 0;
for(ll i = 0; i < n; i++){
if(s.empty())break;
while(a[i] > 0){
auto it = s.upper_bound(i);
if(it == s.end())break;
s.erase(it);
ll j = *it;
ll x = min(a[i],b[j]);
ans+=x;
a[i]-=x;
b[j]-=x;
}
}
for(ll i = 0; i < n; i++){
ans-=max(0ll,b[i] - a[i]);
}
cout << ans;
}
