#include<bits/stdc++.h>
using namespace std;
int n,k,start,end;
int dfs(int now,int s)
{
	if(s==0&&now==end) return 1;
	else if(s==0&&now!=end) return 0;
	else if(now==1) return dfs(2,s-1);
	else if(now==n) return dfs(now-1,s-1);
	else return dfs(now-1,s-1)+dfs(now+1,s-1);
}
int main(){
	cin>>n>>k>>start>>end;
	cout<<dfs(start,k);
}
/**************************************************************
	Problem: 1685
	User: wuyunfeng
	Language: C++
	Result: Compile Error
****************************************************************/