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 JavaScript (node.js v5.12) (judge verdict: Accepted)

/*
-------関数一覧--------
arr1dto2d(Array) 一次元配列を二次元配列にします
pf(N)素因数分解した結果をオブジェクトで返します
gcd(a,b)最大公約数を返します
lcm(a,b)最小公倍数を返します
num(a,b)a-bを返します。ソート用です
isPrime(n)素数かどうか真偽値で返します
isNumber(n)数かどうか真偽値で返します
arrsum(arr)配列の合計値を返します
nibu(arr,n)n以下で最も大きい数の添字を返します(nを含みます)
br(input)入力を改行で区切ります
*/
const debugMode = false;
const inf = Number.MAX_SAFE_INTEGER;

function Main(input){
  input = input.split("\n");
  var sum = 0;
  var a = input[1].split(" ").map(Number);
  var b = input[2].split(" ").map(Number);
 // console.log(a,b)
  for(var i=0;i<b.length;i++){
      if(a[i]>=b[i]){
          sum+=b[i];
      }else if(b[i]-a[i]<=a[i+1]){
          sum+=b[i];
          a[i+1]-=b[i]-a[i];
          
      }else{
          sum += a[i]+a[i+1];
          a[i+1] = 0;
          
      }
    //  console.log(sum)
  }
  console.log(sum);
}Main(require("fs").readFileSync("/dev/stdin", "utf8").trim());