Problem

Consider an N by N chessboard and a knight positioned on cell (a, b) (with

0 ≤ a, b <N). The following question arises, given a positive natural integer k (i.e. k> 0),

how many lengths of k and exclusively within the board boundaries the rider

can take.

Your challenge is to answer this question.

Input Format

The entry for this exercise consists of a line containing the 4 integers N, k, a, and b, separated by

a space.

Output Format

A line with the integer M that indicates how many lengths of k difference are possible

on the board starting from (a, b).

Limits

1 ≤ N ≤ 50 1 ≤ k ≤ 8

Input Example

4 2 0 0

Output Example

8