#include<iostream>
#include<queue>
using namespace std;
int N;
int A[1002],d[1002];
main()
{
	cin>>N>>A[0];
	cin>>A[N+1];
	for(int i=1;i<=N;i++)cin>>A[i];
	queue<int>P;
	P.push(0);
	for(int i=1;i<=N+1;i++)d[i]=1e9;
	while(!P.empty())
	{
		int u=P.front();P.pop();
		for(int j=0;j<=N+1;j++)if(d[j]>d[u]+1&&__builtin_popcount(A[j]^A[u])<=1)
		{
			d[j]=d[u]+1;
			P.push(j);
		}
	}
	int ans=d[N+1];
	if(ans==(int)1e9)ans=0;
	cout<<ans-1<<endl;
}