Codeforces Round #500 (Div. 2) ABC

#include <bits/stdc++.h>

using namespace std;

int n,x;
long long a[200000+10],vis[200000+10];

map<long long,long long>mp;
map<long long,long long>mp1;

int main()
{
    ios::sync_with_stdio(false);cin.tie(0);
    cin>>n>>x;
    mp.clear();
    for(int i=0;i<n;i++){
        cin>>a[i];
        mp[a[i]]++;
    }
    map<long long,long long>::iterator it=mp.begin();


    for(it;it!=mp.end();it++){
        if((it->second)>1){
            cout<<"0"<<endl;
            return 0;
        }
    }

    mp1.clear();int ans=3;
    for(int i=0;i<n;i++){
        int m=a[i]&x;

        if(mp[m]!=0&&m!=a[i])
        {
            ans=min(ans,1);
        }
        else if(mp1[m]!=0){
                ans=min(ans,2);
        }
        else mp1[m]++;
    }

    if(ans==3) cout<<"-1"<<endl;
    else cout<<ans<<endl;

    return 0;
}