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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.lang.reflect.Array;
import java.util.*;
import java.util.Map.*;
import java.io.*;
import java.util.StringTokenizer;
import java.util.stream.Collectors;
import java.util.AbstractMap.SimpleEntry;
import java.util.Comparator;
import java.util.stream.IntStream;

public class Main {

    public static void main(String[] args) {
        FastScanner sc = new FastScanner(System.in);

        int N = sc.nextInt();
        long As[] = sc.nextLongArray(N + 1);
        long Bs[] = sc.nextLongArray(N);
        long sum = 0;

        for(int i = 0; i < N; i++){
             long tmp = Bs[i] < (As[i] + As[i + 1]) ? Bs[i] : (As[i] + As[i + 1]);
             Bs[i] = Bs[i] < tmp ? 0: Bs[i] - tmp;
             sum += tmp;
        }

        System.out.println(sum);
    }

    public static boolean isPrime(long num){
        for(int i = 2; i < num;i++){
            if(num % i == 0)
                return false;
        }
        return true;
    }


    public static long factorial(Long n){
        if(n == 1)
            return 1;
        return n * factorial(n - 1);
    }

    public static <T> HashMap<T,Integer> count_item(T[] target){
        HashMap<T,Integer> hs = new HashMap<>();
        for(T t: target){
            if(hs.containsKey(t))
                hs.put(t,hs.get(t) + 1);
            else
                hs.put(t,1);
        }
        return hs;
    }

    public static class Iterations{

        // nCr を求める
        // 第1引数: 列挙対象の配列 n
        // 第2引数: r
        // 第3引数: 答えの組み合わせ配列を保持するための set
        public static <T> HashSet<ArrayList<T>> combination(ArrayList<T> n, Integer r) {
            HashSet<ArrayList<T>> ans = new HashSet<>();
            Iterations.comb(n,r,ans);
            return ans;
        }


        public static <T> void comb(ArrayList<T> n, Integer r, HashSet<ArrayList<T>> ans) {
            if (n.size() == r) {
                ans.add(n);
                return;
            }

            for (int i = 0; i < n.size(); i++) {
                ArrayList<T> N = new ArrayList<>(n);
                N.remove(i);
                comb(N, r, ans);
            }
        }


        // nPr を求める
        // 第1引数: 列挙対象の配列 n
        // 第2引数: r
        // 第3引数: 答えの組み合わせ配列を保持するための set
        public static <T> List<List<T>> permutation(T[] n,int r) {
            List<T> n_list = Arrays.asList(n);
            HashSet<ArrayList<T>> hs = combination(new ArrayList<>(n_list),r);

            List<List<T>> result = new ArrayList<>();
            for(ArrayList<T> tmp: hs){
                helper(0, tmp, result);
            }
            return result;
        }

        private static <T> void helper(int start, List<T> nums, List<List<T>> result) {
            if (start == nums.size() - 1) {
                ArrayList<T> list = new ArrayList<>();
                for (T num : nums) {
                    list.add(num);
                }
                result.add(list);
                return;
            }

            for (int i = start; i < nums.size(); i++) {
                swap(nums, i, start);
                helper(start + 1, nums, result);
                swap(nums, i, start);
            }
        }

        private static <T> void swap(List<T> nums, int i, int j) {
            T temp = nums.get(i);
            nums.set(i,nums.get(j));
            nums.set(j,temp);
        }
    }


    public static List<Entry<Integer,Integer>> SortMapByValue(HashMap<Integer,Integer> maps,boolean is_reverse){
        List<Entry<Integer,Integer>> entries = new ArrayList<>(maps.entrySet());

        Collections.sort(entries, new Comparator<Entry<Integer, Integer>>() {
            @Override
            public int compare(Entry<Integer, Integer> o1, Entry<Integer, Integer> o2) {
                return (is_reverse ? -1 : 1) * o1.getValue().compareTo(o2.getValue());
            }
        });

        return entries;
    }

    public static long max(int[] ar,int size){
        long max = 0;
        for(int i = 0; i< size;i++)
            if(max < ar[i])
                max = ar[i];
        return max;
    }


    public static long max(List<Long> ar){
        long max = 0;
        for(int i = 0; i< ar.size();i++)
            if(max < ar.get(i))
                max = ar.get(i);
        return max;
    }

    public static Integer min(List<Integer> ar){
        int min = 10000;
        int index = 0;
        for(int i = 0; i< ar.size();i++){
            if(min > ar.get(i)){
                min = ar.get(i);
                index = i;
            }
        }
        return min;
    }

    // 最大公約数を求める
    public static <T extends Number> Long gcd(T left, T right) {
        Long m = left.longValue();
        Long n = right.longValue();
        if(m == 0)
            return n;
        if(n == 0)
            return m;
        if(m < n) return gcd(n, m);
        if(n == 0) return m;
        return gcd(n, m % n);
    }

    // 最小公倍数を求める
    public static <T extends Number> Long lcm(T left, T right){
        return left.longValue() * right.longValue() / gcd(left,right);
    }

    // A 以上、B 以下のCの倍数の個数を考える (A <= B)
    public static <T extends Number> Long get_multiple_count(T A, T B,T C){
        Long b_multi = B.longValue() / C.longValue();
        Long a_multi = (A.longValue() - 1) / C.longValue();
        return b_multi - a_multi;
    }



    static class FastScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public String[] nextArray(int n) {
            String[] a = new String[n];
            for (int i = 0; i < n; i++)
                a[i] = next();
            return a;
        }


        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
    }

    public static class SizeComparator implements Comparator<HashSet>{
        @Override
        public int compare(HashSet l1, HashSet l2){
            return l1.size() > l2.size() ? -1 : 1;
        }
    }

}