#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define REP(i,n)   FOR(i,0,n)

#define DUMP(var) std::cout << #var " = " << var << std::endl;

#define PRINT(os, c)                              \
  do {                                            \
    os << "[ ";                                   \
    for (auto i = c.begin(); i != c.end(); i++) { \
      if (i != c.begin()) {                       \
        os << ", ";                               \
      }                                           \
      os << *i;                                   \
    }                                             \
    os << " ]";                                   \
    return os;                                    \
  } while (0)
#define PRINT_MAP(os, c)                          \
  do {                                            \
    os << "{ ";                                   \
    for (auto i = c.begin(); i != c.end(); i++) { \
      if (i != c.begin()) {                       \
        os << ", ";                               \
      }                                           \
      os << (*i).first << " => " << (*i).second;  \
    }                                             \
    os << " }";                                   \
    return os;                                    \
  } while (0)
#define PRINT_SET(os, c)                          \
  do {                                            \
    os << "( ";                                   \
    for (auto i = c.begin(); i != c.end(); i++) { \
      if (i != c.begin()) {                       \
        os << ", ";                               \
      }                                           \
      os << *i;                                   \
    }                                             \
    os << " )";                                   \
    return os;                                    \
  } while (0)

template <typename T>
std::ostream& operator<<(std::ostream& os, const std::vector<T>& c) {
  PRINT(os, c);
}
template <typename T>
std::ostream& operator<<(std::ostream& os, const std::deque<T>& c) {
  PRINT(os, c);
}
template <typename T>
std::ostream& operator<<(std::ostream& os, const std::list<T>& c) {
  PRINT(os, c);
}
template <typename T>
std::ostream& operator<<(std::ostream& os, const std::forward_list<T>& c) {
  PRINT(os, c);
}
template <typename T, typename U>
std::ostream& operator<<(std::ostream& os, const std::map<T, U>& c) {
  PRINT_MAP(os, c);
}
template <typename T, typename U>
std::ostream& operator<<(std::ostream& os, const std::multimap<T, U>& c) {
  PRINT_MAP(os, c);
}
template <typename T, typename U>
std::ostream& operator<<(std::ostream& os, const std::unordered_map<T, U>& c) {
  PRINT_MAP(os, c);
}
template <typename T, typename U>
std::ostream& operator<<(std::ostream& os,
                         const std::unordered_multimap<T, U>& c) {
  PRINT_MAP(os, c);
}
template <typename T>
std::ostream& operator<<(std::ostream& os, const std::set<T>& c) {
  PRINT_SET(os, c);
}
template <typename T>
std::ostream& operator<<(std::ostream& os, const std::multiset<T>& c) {
  PRINT_SET(os, c);
}
template <typename T>
std::ostream& operator<<(std::ostream& os, const std::unordered_set<T>& c) {
  PRINT_SET(os, c);
}
template <typename T>
std::ostream& operator<<(std::ostream& os,
                         const std::unordered_multiset<T>& c) {
  PRINT_SET(os, c);
}
template <typename T, typename U>
std::ostream& operator<<(std::ostream& os, const std::pair<T, U>& p) {
  os << "< " << p.first << ", " << p.second << " >";
  return os;
}

int main() {
  ll N;
  cin>>N;
  vector<ll> A(N+1,0);
  vector<ll> B(N,0);
  REP(i,N+1)cin>>A[i];
  REP(i,N)cin>>B[i];
  ll ans = 0;
  REP(i,N){
    ll tmp = min(A[i],B[i]);
    ans+=tmp;
    A[i]-=tmp;
    B[i]-=tmp;

    tmp = min(A[i+1],B[i]);
    ans+=tmp;
    A[i+1]-=tmp;
    B[i]-=tmp;
  }
  cout<<ans<<endl;


  return 0;
}


Measured memory_bytes: 1792