#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main(){
cin.tie(0);
ios::sync_with_stdio(0);
ll n;
cin >> n;
vector<ll> slots(n);
vector<ll> ppl(n);
for(ll i = 0; i < n; i++) cin >> slots[i];
for(ll i = 0; i < n; i++) cin >> ppl[i];
// do upgrades
ll score = 0;
ll curr_ppl = n - 1;
for(ll i = n - 2; i >= 0; i--){
// if we've run out of ppl beneath us to upgrade, continue
if(ppl[curr_ppl] == 0) curr_ppl--;
if(curr_ppl <= i) continue;
// assign these slots
ll remove = min(slots[i], ppl[curr_ppl]);
slots[i] -= remove;
ppl[curr_ppl] -= remove;
score += remove;
}
// do samegrades
for(ll i = 0; i < n; i++){
ll remove = min(slots[i], ppl[i]);
slots[i] -= remove;
ppl[i] -= remove;
}
// do downgrades
for(ll i = 0; i < n; i++) score -= ppl[i];
cout << score << "\n";
}
