package 基本算法;
import java.util.Arrays;
import java.util.Scanner;
public class 二分法_1 {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc=new Scanner(System.in);
int n=sc.nextInt();
int K=sc.nextInt();
int[] ch=new int[n];
for(int i=0;i<n;i++) {
ch[i]=sc.nextInt();
}
int index=find(ch,K);
System.out.println(index);
}
private static int find(int[] ch, int k) {
// TODO Auto-generated method stub
int l=-1,r=ch.length-1;
while(r-l>1) {
int mid=(l+r)/2;
if(ch[mid]>=k) {
r=mid;
}else {
l=mid;
}
}
if(ch[r]==k) {
return r;
}else {
return -1;
}
}
}
