[Codeforces 1013B] And

#include<bits/stdc++.h>
using namespace std;
#define MAXN 100010

int i,n,x;
int a[MAXN];
map<int,int> mp;

int main() 
{
        
        scanf("%d%d",&n,&x);
        for (i = 1; i <= n; i++) 
        {
                scanf("%d",&a[i]);
                mp[a[i]]++;
        }
        for (i = 1; i <= n; i++)
        {
                if (mp[a[i]] >= 2)
                {
                        printf("0\n");
                        return 0;
                }
        }
        for (i = 1; i <= n; i++)
        {
                if ((a[i] & x) == a[i]) continue;
                if (mp[a[i] & x] >= 1)
                {
                        printf("1\n");
                        return 0;
                }
        }
        mp.clear();
        for (i = 1; i <= n; i++) a[i] &= x;
        for (i = 1; i <= n; i++) mp[a[i]]++;
        for (i = 1; i <= n; i++)
        {
                if (mp[a[i]] >= 2)
                {
                        printf("2\n");
                        return 0;
                }
        }
        printf("-1\n");
        
        return 0;
    
}