//greedily make the ppl at the back happi first
#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main() {
int n; cin >> n;
int a[n]; for (int i = 0; i < n; i++) cin >> a[i];
int b[n]; for (int i = 0; i < n; i++) cin >> b[i];
set<pair<int,int>> ok;
for (int i = 0; i < n; i++) if (a[i] > 0) ok.insert({i,b[i]});
int ans=0;
for (int i = 0; i < n; i++) {
//make these ppl happy by allocating them to the first that they can go
int cur = a[i];
while (cur>0&&ok.size()) {
auto itr = ok.lower_bound({i+1,0});
if (itr == ok.end()) {
//then too bad, we have to go neutral.
itr = ok.lower_bound({i,0});
if (itr == ok.end()) {
//too bad lol you have to make someone cry now.
break;
}
else {
auto store = *itr;
int take = min((*itr).second, cur);
if (take==(*itr).second) {ok.erase(itr); cur-=take;}
else {ok.erase(itr); ok.insert({store.first, store.second-take});cur-=take;}
}
}
else {
auto store = *itr;
int take = min(cur,store.second);
ans += take;
if (store.second==take) {ok.erase(itr); cur -= take;}
else {ok.erase(itr); ok.insert({store.first, store.second-take});cur-=take;
}
}
}
}
for (auto i:ok) ans -= i.second;
cout << ans;
//now that they are all happy, we can make everyone else sad.
}
