/* package whatever; // don't place package name! */

import java.util.*;
class Main{
	public static void main(String[]args){
		Scanner sc = new Scanner(System.in);
		int n= sc.nextInt();int tar = sc.nextInt();
		int [] arr = new int[n];
		for(int i=0; i<n; i++){
			arr[i] = sc.nextInt();
		}
		Arrays.sort(arr);
		int st = 0; int end = n-1;
		
		while(st<=end){
			int mid = st + (end-st)/2;
			if(tar<arr[mid]){
				end = mid-1;
			}else if(tar>arr[mid]){
				st = mid+1;
			}else{
				System.out.println(mid);
				return;
			}
		}
		System.out.println(-1);
	}
}