#include<bits/stdc++.h>
using namespace std;
int a,n,m,x,k,shu[100],up[100],ans=0; 
bool f(int p,int s,int num)//人数，站数，第二站上车人数 
{
	s++;
	if(s==n)
	{
		if(p==m)
		{
			k=num;
			return 0;
		}
		else
		{
			ans=0;
			return 1;
		}
	}
	up[s]=up[s-2]+up[s-1];
	p=shu[s]=shu[s-1]+up[s]-up[s-1];
	if(s==x) ans=p;
	if(s<n) f(p,s,num);
}
int main()
{
	cin >> a >> n >> m >> x;
	int i=1,j=2;
	shu[1]=a,shu[2]=a,up[1]=a,up[2]=i;
	while(f(a,j,i))
	{
		j=2,i++;
		memset(shu,0,sizeof(shu));
		memset(up,0,sizeof(up));
		shu[1]=a,shu[2]=a,up[1]=a,up[2]=i;
	} 
	cout << ans;
    return 0;
}