//https://www.codechef.com/CCSTART2/problems/FINDMELI
class Codechef
{
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
long arr[] = new long[sc.nextInt()];
long k = sc.nextInt();
boolean bool = true;
for (int i = 0; i < arr.length; i++) {
arr[i] = sc.nextInt();
}
for (int j = 0; j < arr.length; j++) {
if (arr[j] == k) {
System.out.println(1);
bool = false;
}
}
if (bool) {
for (int j = 0; j < arr.length; j++) {
if (arr[j] != k) {
System.out.println(-1);
break;
}
}
}
sc.close();
}
}