//~~~~~~~~~~~~~MJ®™~~~~~~~~~~~~~
#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#define rep1(n) for(ll i=0; i<(ll)(n); ++i)
#define rep2(i,n) for(ll i=0; i<(ll)(n); ++i)
#define rep3(i,a,b) for(ll i=(ll)(a); i<(ll)(b); ++i)
#define rep4(i,a,b,c) for(ll i=(ll)(a); i<(ll)(b); i+=(c))
#define cut4(a,b,c,d,e,...) e
#define rep(...) cut4(__VA_ARGS__,rep4,rep3,rep2,rep1)(__VA_ARGS__)
#define per1(n) for(ll i=((ll)n)-1; i>=0; --i)
#define per2(i,n) for(ll i=((ll)n)-1; i>=0; --i)
#define per3(i,a,b) for(ll i=((ll)a)-1; i>=(ll)(b); --i)
#define per4(i,a,b,c) for(ll i=((ll)a)-1; i>=(ll)(b); i-=(c))
#define per(...) cut4(__VA_ARGS__,per4,per3,per2,per1)(__VA_ARGS__)
#define ll long long
#define ln cout<<endl
#define int long long
#define vv vector<vi>
#define vp vector<pi>
#define append push_back
#define all(x) (x).begin(),(x).end()
#define allr(x) (x).rbegin(),(x).rend()
#define vi vector<int>
#define ret(x) {cout<<x;return;}
#define ui map<int,int>
#define pi pair<int,int>
#define ff first
#define ss second
using namespace std;
const int INF = 1e18, MOD = 1e9+7, N = 2e5+7;
void solve()
{
int n, k, e, m, ans = 0;
cin >> n;
vi a(n);
vi l(n);
int nowslot = 0;
int prevslot = 0;
int nowmen = 0;
int prevmen = 0;
rep(n)
{
cin >> a[i];
}
rep(n)
{
cin>> l[i];
}
vi suffix(n+1,0);
per(n)
{
suffix[i] = suffix[i+1] + l[i];
}
rep(n)
{
nowslot = a[i];
nowmen = l[i];
ans+=min(prevslot, nowmen);
nowmen-=min(prevslot, nowmen);
int now = min({nowmen, nowslot});
// cout << "debug: " << now << " " << suffix[i+1];ln;
now = max(now - suffix[i+1] , 0ll);
nowmen-=now;
nowslot-=now;
// cout << "debug: " << nowslot << " " << nowmen << " " << ans;ln;
if (nowmen>0)
{
ans-= nowmen;
}
// cout << "debug: " << now << " " << ans;ln;
prevslot = nowslot;
}
cout << ans;
// cout << a.size();
// for (auto i: a){cout << i << " ";}
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL); cout.tie(NULL);
int ans=1;
//cout<<setprecision(1000);
// cin>>ans;
rep(ans){
// cout << "Case #" << i+1 << ": ";
solve();ln;}}
