#include <iostream>
using namespace std;
int main()
{
	long long int dp[20][20]={0};
	int horse[24][24]={0};
	int bn,bm,hn,hm;
	cin>>bn>>bm>>hn>>hm;
	hn=hn+2;
	hm=hm+2;
	horse[hn][hm]=horse[hn+2][hm+1]=horse[hn+1][hm+2]=
	horse[hn-1][hm+2]=horse[hn-2][hm+1]=horse[hn-2][hm-1]=horse[hn-1][hm-2]=
	horse[hn+1][hm-2]=horse[hn+2][hm-1]=1;
	int i=0,j=0;
	while(horse[2][i+2]!=1&&i<=bm)	dp[0][i++]=1;
	while(horse[j+2][2]!=1&&j<=bn)	dp[j++][0]=1;
	for(int x=1;x<=bn;x++)
	{
		for(int y=1;y<=bm;y++)
		{
			if(horse[x+2][y+2]!=1)	dp[x][y]=dp[x-1][y]+dp[x][y-1];
		}
	}
	cout<<dp[bn][bm];
  return 0;
}