import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		int N=30;
		Scanner sc=new Scanner(System.in);
		int[][] f=new int[N][N];
		int[][] d=new int[N][N];
		
		int p=sc.nextInt();
		p=p+2;
		int q=sc.nextInt();
		q=q+2;
		int r=sc.nextInt();
		r=r+2;
		int z=sc.nextInt();
		z=z+2;
		plug(d, r, z);
		f[1][2]=1;
		for(int i=2;i<=p;i++) {
			for(int j=2;j<=q;j++) {
				if(d[i][j]==0&&d[i][j]==0) {
					f[i][j]=f[i-1][j]+f[i][j-1];
				}
								
			}
		}
	System.out.println(f[p][q]);

	}
	public static void plug(int[][]arr,int i,int j) {
		arr[i][j]=1;
		arr[i-1][j-2]=1;
		arr[i-1][j+2]=1;
		arr[i+1][j-2]=1;
		arr[i+1][j+2]=1;
		arr[i-2][j-1]=1;
		arr[i-2][j+1]=1;
		arr[i+2][j-1]=1;
		arr[i+2][j+1]=1;	
	}

}