#include <bits/stdc++.h>
using namespace std;

# define REP(i,n) for (int i=0;i<(n);++i)
# define rep(i,a,b) for(int i=a;i<(b);++i)
# define p(s) std::cout << s ;
# define pl(s)  std::cout << s << endl;
# define printIf(j,s1,s2) cout << (j ? s1 : s2) << endl;
# define YES(j) cout << (j ? "YES" : "NO") << endl;
# define Yes(j) std::cout << (j ? "Yes" : "No") << endl;
# define yes(j) std::cout << (j ? "yes" : "no") << endl;
# define all(v) v.begin(),v.end()
# define showVector(v) REP(i,v.size()){p(v[i]);p(" ")} pl("")
template<class T> inline bool chmin(T &a, T b){ if(a > b) { a = b; return true;} return false;}
template<class T> inline bool chmax(T &a, T b){ if(a < b) { a = b; return true;} return false;}
typedef long long int ll;
typedef pair<ll,ll> P_ii;
typedef pair<double,double> P_dd;

template<class T>
vector<T> make_vec(size_t a){
    return vector<T>(a);
}

template<class T, class... Ts>
auto make_vec(size_t a, Ts... ts){
  return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

template<typename T,typename V>
typename enable_if<is_class<T>::value==0>::type
fill_v(T &t,const V &v){t=v;}

template<typename T,typename V>
typename enable_if<is_class<T>::value!=0>::type
fill_v(T &t,const V &v){
  for(auto &e:t) fill_v(e,v);
}


const int MOD = 1000000007;
const int inf=1e9+7;
const ll longinf=1LL<<60 ;

void addM(long long &a, long long b) {
    a += b;
    if (a >= MOD) a -= MOD;
}

void mulM(long long &a, long long b) {
    a = ((a%MOD)*(b%MOD))%MOD ;
}

const int MAX = 510000;
long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}

// 二項係数計算
long long COM(int n, int k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

vector<pair<long long, long long> > prime_factorize(long long n) {
    vector<pair<long long, long long> > res;
    for (long long p = 2; p * p <= n; ++p) {
        if (n % p != 0) continue;
        int num = 0;
        while (n % p == 0) { ++num; n /= p; }
        res.push_back(make_pair(p, num));
    }
    if (n != 1) res.push_back(make_pair(n, 1));
    return res;
}

long long int gcd(long long int a,long long int b){
    if(a<b){
        long long int tmp=a;
        a=b;
        b=tmp;
    }

    long long int r = a % b;
    while(r!=0){
        a = b;
        b = r;
        r = a % b;
    }
    return b;
}

long long int lcm(long long int a,long long int b){
    long long int g = gcd(a,b);
    return (a/g)*b;
}


int main() {
    int n;
    cin >> n;

    vector<ll> a1(n+1);
    vector<ll> a2(n+1);
    REP(i,n+1) {
        cin >> a1[i];
        a2[i] = a1[i];
    }

    vector<ll> b(n);
    REP(i,n) cin >> b[i];

    ll ans1 = 0;
    REP(i,n){
        if(a1[i] < b[i]) {
            ans1 += a1[i];
            if(a1[i+1] < (b[i] - a1[i])){
                ans1 += a1[i+1];
                a1[i+1] = 0;
            } else {
                ans1 += (b[i] - a1[i]);
                a1[i+1] -= (b[i] - a1[i]);
            }
            a1[i] = 0;
        } else {
            ans1 += b[i];
            a1[i] -= b[i];
        }
    }

    ll ans2 = 0;
    for(int i = n-1; i >= 0; i--){
        if(a2[i+1] < b[i]) {
            ans2 += a2[i+1];
            if(a2[i] < (b[i] - a2[i+1])){
                ans2 += a2[i];
                a2[i] = 0;
            } else {
                ans2 += (b[i] - a2[i+1]);
                a2[i] -= (b[i] - a2[i+1]);
            }
            a2[i+1] = 0;
        } else {
            ans2 += b[i];
            a2[i+1] -= b[i];
        }
    }

    pl(max(ans1,ans2))

    return 0;
}

Measured memory_bytes: 2688