## Bon Appétit

November 09, 2017

Anna and Brian order $n$ items at a restaurant, but Anna declines to eat any of the $k^{th}$ item (where $0 \le k \lt n$) due to an allergy. When the check comes, they decide to split the cost of all the items they shared; however, Brian may have forgotten that they didn’t split the $k^{th}$ item and accidentally charged Anna for it.

You are given $n$, $k$, the cost of each of the $n$ items, and the total amount of money that Brian charged Anna for her portion of the bill. If the bill is fairly split, print Bon Appetit; otherwise, print the amount of money that Brian must refund to Anna.

Input Format

The first line contains two space-separated integers denoting the respective values of $n$ (the number of items ordered) and $k$ (the 0-based index of the item that Anna did not eat).

The second line contains $n$ space-separated integers where each integer $i$ denotes the cost, $c[i]$, of item $i$ (where $0 \le i \lt n$).

The third line contains an integer, $b_{charged}$, denoting the amount of money that Brian charged Anna for her share of the bill.

Constraints

Output Format

If Brian did not overcharge Anna, print Bon Appetit on a new line; otherwise, print the difference (i.e., $b_{charged} - b_{actual}$) that Brian must refund to Anna (it is guaranteed that this will always be an integer).

Sample Input 0

4 1

3 10 2 9

12

Sample Output 0

5

__Explanation 0 __

Anna didn’t eat item $c[i]=10$, but she shared the rest of the items with Brian. The total cost of the shared items is $3 + 2 + 9 = 14$ and, split in half, the cost per person is $b_{actual}=7$. Brian charged her $b_{charged}=12$ for her portion of the bill, which is more than the $7$ dollars worth of food that she actually shared with him. Thus, we print the amount Anna was overcharged, $b_{charged} - b_{actual} = 12 - 7 = 5$, on a new line.

Sample Input 1

4 1

3 10 2 9

7

Sample Output 1

Bon Appetit

__Explanation 1 __

Anna didn’t eat item $c[i]=10$, but she shared the rest of the items with Brian. The total cost of the shared items is $3+2+9=14$ and, split in half, the cost per person is $b_{actual}=7$. Because this matches the amount, $b_{charged}$, that Brian charged Anna for her portion of the bill, we print Bon Appetit on a new line.