#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i,n) for(int i=0;i<n;i++)
#define int long long
static const int INF=1000000007;

int cb(int i,int j){
  int ck=(i^j);
  int cnt=0;
  while(ck){
    cnt+=ck%2;
    ck/=2;
  }
  if(cnt==1||cnt==0) return 1;
  else return 0;
}
    
signed main(){
  int n;
  cin>>n;
  int x[n+2];
  cin>>x[0]>>x[n+1];
  rep(i,n) cin>>x[i+1];
  vector<int>a[n+2];
  rep(i,n+2) rep(j,n+2){
    if(i == j) continue;
    int cnt=0;
    if(cb(x[i],x[j])==1) a[i].push_back(j);
  }
  if(cb(x[0],x[n+1])==1){
    cout<<0<<endl;
    return 0;
  }
  vector<int>d(n+2,INF);
  queue<int>que;
  que.push(0);
  d[0]=0;
  while(!que.empty()){
    int u=que.front();
    que.pop();
    for(auto v:a[u]){
      if(d[v] != INF) continue;
      d[v]=d[u]+1;
      que.push(v);
    }
  }
  if(d[n+1]==INF){
    cout<<-1<<endl;
    return 0;
  }
  else{
    cout<<d[n+1]-1<<endl;
  }
  return 0;
}