#include<iostream>
using namespace std; 
#define ll long long
ll f[30][30];
bool ctrl[30][30];
const int d[8][2]={{1,2},{-1,2},{1,-2},{-1,-2},{2,1},{-2,1},{2,-1},{-2,-1}};
int main(){
	int bx,by,dx,dy;
	cin>>bx>>by>>dx>>dy;
	for(int i=0;i<8;i++){
		int xx=dx+d[i][0];
		int yy=dy+d[i][1];
		if(xx>=0&&yy>=0&&xx<=bx&&yy<=by)
			ctrl[xx][yy]=1;
	}
	for(int i=1;i<=bx;i++){
		for(int j=1;j<=by;j++){
			if(ctrl[i][j]) continue;
			if(i!=0) f[i][j]+=f[i-1][j];
			if(j!=0) f[i][j]+=f[i][j-1];
		}
	} 
	cout<<f[bx][by];
	return 0;
}