Problem:
Score : 300 points

Problem Statement

There are N+1 towns. The i-th town is being attacked by A_i monsters.

We have N heroes. The i-th hero can defeat monsters attacking the i-th or (i+1)-th town, for a total of at most B_i monsters.

What is the maximum total number of monsters the heroes can cooperate to defeat?

Constraints

All values in input are integers.

1 \leq N \leq 10^5

1 \leq A_i \leq 10^9

1 \leq B_i \leq 10^9

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_{N+1}
B_1 B_2 ... B_N

Output

Print the maximum total number of monsters the heroes can defeat.

Sample Input 1

2
3 5 2
4 5

Sample Output 1

9

If the heroes choose the monsters to defeat as follows, they can defeat nine monsters in total, which is the maximum result.

The first hero defeats two monsters attacking the first town and two monsters attacking the second town.

The second hero defeats three monsters attacking the second town and two monsters attacking the third town.

Sample Input 2

3
5 6 3 8
5 100 8

Sample Output 2

22

Sample Input 3

2
100 1 1
1 100

Sample Output 3

3

Solution in C++ (GCC 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define int long long
#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename \
  enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; };
sim > rge<c> range(c i, c j) { return rge<c> {i, j}; }
sim > auto dud(c* x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifndef LOCAL
	~debug() { cerr << endl; }
	eni( != ) cerr << boolalpha << i; ris;
}
eni( == ) ris << range(begin(i), end(i));
}
sim, class b dor(pair < b, c > d) {
	ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
	*this << "[";
	for (auto it = d.b; it != d.e; ++it)
		*this << ", " + 2 * (it == d.b) << *it;
	ris << "]";
}
#else
	sim dor(const c&) { ris; }
#endif
};
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
template <typename T>
using indexed_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define int long long
#define ld long double
#define pb push_back
#define mp make_pair
#define in insert
#define fi first
#define se second
#define lb lower_bound
#define ub upper_bound
#define mod 1000000007
#define sz(v) (int)(v.size())
#define all(x) x.begin(), x.end()
#define prec fixed << setprecision(12)
#define rep(i, a, b) for (int i = a; i <= b; ++i)
#define repr(i, a, b) for(int i = a; i >= b; i--)
#define test int t; cin >> t; while(t--)
typedef vector<int> vi;
typedef pair<int, int> pii;
typedef set<int> si;
typedef map<int, int> mii;
typedef vector<pii> vpi;
int _x[] = {0, 0, -1, 1, -1, 1, -1, 1};
int _y[] = { -1, 1, 0, 0, 1, -1, -1, 1};

void solve() {
    int n;
    cin >> n;
    vi a(n+1), b(n);
    rep(i, 0, n) cin >> a[i];
    rep(i, 0, n-1) cin >> b[i];
    int ans = 0;
    rep(i, 0, n-1){
        debug() << imie(a[i]) imie(b[i]) imie(ans);
        if(b[i] >= a[i]){
            ans += a[i];
            b[i]-=a[i];
            a[i] = 0;
        }else{
            ans += b[i];
            a[i]-=b[i];
            b[i] = 0;
        }
        if(b[i] >= a[i+1]){
            ans += a[i+1];
            b[i] -= a[i+1];
            a[i+1] = 0;
        }else{
            ans += b[i];
            a[i+1] -= b[i];
            b[i] = 0;
        }
    }
    cout << ans << "\n";
}

signed main() {
    ios::sync_with_stdio(false); cin.tie(NULL);
	// test
	solve();
	return 0;
}