Pair of Toys

Description:

Input:

The first line of the input contains two integers $$$n$$$, $$$k$$$ ($$$1 \le n, k \le 10^{14}$$$) — the number of toys and the expected total cost of the pair of toys.

Output:

Print the number of ways to choose the pair of toys satisfying the condition above. Print 0, if Tanechka can choose no pair of toys in such a way that their total cost is $$$k$$$ burles.

Sample Input:

8 5

Sample Output:

2

Sample Input:

8 15

Sample Output:

1

Sample Input:

7 20

Sample Output:

0

Sample Input:

1000000000000 1000000000001

Sample Output:

500000000000

Note:

In the first example Tanechka can choose the pair of toys ($$$1, 4$$$) or the pair of toys ($$$2, 3$$$).

In the second example Tanechka can choose only the pair of toys ($$$7, 8$$$).

In the third example choosing any pair of toys will lead to the total cost less than $$$20$$$. So the answer is 0.

In the fourth example she can choose the following pairs: $$$(1, 1000000000000)$$$, $$$(2, 999999999999)$$$, $$$(3, 999999999998)$$$, ..., $$$(500000000000, 500000000001)$$$. The number of such pairs is exactly $$$500000000000$$$.