#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++){
		dx+=d[i][0];
		dy+=d[i][1];
		if(dx>=0&&dy>=0&&dx<=bx&&dx<=by)
			ctrl[dx][dy]=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;
}