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.util.*;

public class Main {

    public static void main(String[] args) {

        Scanner parameter = new Scanner(System.in);

        String[] input1 = parameter.nextLine().split(" ");
        String[] input2 = parameter.nextLine().split(" ");
        String[] input3 = parameter.nextLine().split(" ");

        // 倒す数を累計する
        Integer countKillMoster = 0;

        // 勇者の人数分でループする
        for (int i = 0; i < input3.length; i++) {

            // ループされてる勇者が何頭倒せる引数
            Integer killNoOfMoster = Integer.valueOf(input3[i]);
            // 勇者に該当する街道のモンスター数
            Integer noOfMosterThisStreet = Integer.valueOf(input2[i]);

            // 勇者がモンスターを倒せる数と該当する街道のモンスター数を比較する
            if (killNoOfMoster <= noOfMosterThisStreet) {

                // 該当街道のモンスターを総数に加える
                countKillMoster = countKillMoster + killNoOfMoster;
            } else {

                // 次の街道のモンスター数
                Integer noOfmosterNextStreet = Integer.valueOf(input2[i + 1]);
                // 二街道全部のモンスター数
                Integer totalMoster = noOfMosterThisStreet + noOfmosterNextStreet;

                // 倒せるモンスター数が二街道総数より多く場合
                if (killNoOfMoster >= totalMoster) {

                    // ２街道纏めて総数に加える
                    countKillMoster = countKillMoster + totalMoster;
                    // 街道２のモンスター数を0にする
                    input2[i + 1] = "0";
                } else {

                    // 倒せたモンスター数を加える
                    countKillMoster = countKillMoster + (killNoOfMoster - noOfMosterThisStreet);
                    // 街道２の残ったモンスター数を計算する
                    input2[i + 1] = String.valueOf(totalMoster - killNoOfMoster);
                }
            }
        }

        System.out.println(countKillMoster);
    }
}