P1002 过河卒

import java.util.Scanner;

public class Main{
    static int hl[][]=new int[20][20];
    static int sum=0;
    static int blx,bly;
    public static void unreach(int hx,int hy){
        hl[hx][hy]=hl[hx+1][hy+2]=hl[hx+2][hy+1]=hl[hx+2][hy-1]=hl[hx+1][hy-2]=hl[hx-1][hy-2]
                =hl[hx-2][hy-1]=hl[hx-2][hy+1]=hl[hx-1][hy+2]=1;
    }
    public static void count(int sx,int sy){
        if(hl[sx][sy]==1||sx>blx||sy>bly){
            return;
        }
        if(sx==blx&&sy==bly){
            sum++;
            return;
        }
        count(sx+1,sy);
        count(sx,sy+1);
    }
    public static void main(String args[]){
        Scanner sc=new Scanner(System.in);
        int bx,by,hx,hy;
        bx=sc.nextInt();
        by=sc.nextInt();
        blx=bx;
        bly=by;
        hx=sc.nextInt();
        hy=sc.nextInt();
        unreach(hx,hy);
        count(0,0);
        System.out.println(sum);
    }
}