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 PHP (5.6.30) (judge verdict: Wrong Answer)

import glob


# 問題ごとのディレクトリのトップからの相対パス
REL_PATH = 'ABC\\135\\C'

# テスト用ファイル置き場のトップ
TOP_PATH = 'C:\\AtCoder'


class Common:

    problem = []
    index = 0

    def __init__(self, rel_path):
        self.rel_path = rel_path

    def initialize(self, path):
        file = open(path)
        self.problem = file.readlines()
        self.index = 0
        return

    def input_data(self):
        try:
            IS_TEST
            self.index += 1
            return self.problem[self.index-1]

        except NameError:
            return input()

    def resolve(self):
        pass

    def exec_resolve(self):
        try:
            IS_TEST
            for path in glob.glob(TOP_PATH + '\\' + self.rel_path + '/*.txt'):
                print("Test: " + path)
                self.initialize(path)
                self.resolve()
                print("\n\n")
        except NameError:
            self.resolve()


class C(Common):

    def resolve(self):

        N = int(self.input_data())
        monster = [int(i) for i in self.input_data().split()]
        saver = [int(i) for i in self.input_data().split()]

        result = 0
        remaining = 0

        for i in range(N):
            if saver[i] + remaining > monster[i]:
                result += monster[i]
                remaining = saver[i] + remaining - monster[i]
                if remaining > saver[i]:
                    remaining = saver[i]
            else:
                result += saver[i] + remaining
                remaining = 0

        if remaining > monster[N]:
            result += monster[N]
        else:
            result += remaining

        print(str(result))


solver = C(REL_PATH)
solver.exec_resolve()