#include <iostream>
#include <cstring>
using namespace std;
int ex,ey; //B坐标 
int hx,hy; //马坐标 
int f[35][35];
int dir[9][2] = {{0},{-2,1},{-1,2},{1,2},{2,1},{2,-1},{1,-2},{-1,-2},{-2,-1}};
int main() {
	memset(f,-1,sizeof(f));
//	cout << s[1][1];
	cin >> ex >> ey >> hx >> hy;
	for (int i = 1; i <= ex; i++) f[i][0] = 1;
	for (int i = 1; i <= ey; i++) f[0][i] = 1;
	f[hx][hy] = 0;
	for (int i = 1; i <= 8; i++) {
		int nx = hx + dir[i][0];
		int ny = hy + dir[i][1];
		f[nx][ny] = 0;
//		cout << nx << ' ' << ny << endl;
	}
/*	for (int i = 0; i <= ex; i++) {
		for (int j = 0; j <= ey; j++) {
			cout << f[i][j] << ' ';
		}
		cout << endl;
	}*/
	for (int i = 1; i <= ex; i++) {
		for (int j = 1; j <= ey; j++) {
			if (f[i][j] != 0) {
				f[i][j] = f[i - 1][j] + f[i][j - 1];
			}
		}
	}/*
	for (int i = 1; i <= ex; i++) {
		for (int j = 1; j <= ey; j++) {
			cout << f[i][j] << ' ';
		}
		cout << endl;
	}*/
	cout << f[ex][ey] << endl;
	return 0;
} 

#3 #4 WA了