#include<iostream>
using namespace std;
int N;
long M,A[80];
main()
{
	cin>>N>>M;
	A[0]=A[1]=1;
	int ans=0;
	for(int i=2;i<N;i++)
	{
		A[i]=A[i-1]+A[i-2];
		A[i]--;
		for(int k=i+1;k<N;k++)
		{
			A[k]=A[k-1]+A[k-2];
		}
		if(A[N-1]>=M)ans++;
		else A[i]++;
	}
	if(A[N-1]==M)cout<<ans<<endl;
	else cout<<-1<<endl;
}