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.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int A[] = new int[N+1];
		int B[] = new int[N];
		int Ai;
		//　モンスターの撃退数
		int count = 0;
		//trueのとき前の勇者gまだ倒せる
		boolean jud;
		
		//input
		for(int i=0;i<=N;i++) {
			A[i] = sc.nextInt();
		}
		for(int i=0;i<N;i++) {
			B[i] = sc.nextInt();
		}
		//method
		
		if(A[0] >= B[0]){
			count = B[0];
			jud = false;
		}else {
			B[0] = B[0] - A[0];
			count = A[0];
			jud = true;
		}
		
		for(int i=1;i<N;i++) {
			if(jud) {
				Ai = A[i] - B[i-1];
				//　前の勇者が倒してまだ残っている＆残りのモンスター数が今の勇者が倒せる数より大きい→モンスターが残る
				if(Ai >= 1 && Ai >= B[i]){
					count = count + B[i-1]+B[i];
					jud = false;
				}//残りのモンスターが今の勇者が倒せる数より小さい→今の勇者の残数を次に持ちこし
				else if(Ai >= 1 && Ai < B[i]) {
					count = count + A[i];
					B[i] = B[i] - Ai;
					jud = true;
				}//　前の勇者の残りで全てのモンスターを倒せた場合
				else{
					count = count + A[i];
					jud = true;
				}
			}//前の勇者の数が残っていない場合
			else {
				if(A[i] >= B[i]) {
					count = count + B[i];
					jud = false;
				}else {
					B[i] = B[i] - A[i];
					count = count + A[i];
					jud = true;
				}
			}
		}
		
		if(jud){
			if(A[N] < B[N-1]) {
				count = count + A[N];
			}else {
				count = count + B[N-1];
			}
		}
		
		System.out.println(count);
	}
}