#include<bits/stdc++.h>
using namespace std;
int main(){
	long long n,a[1000000]={0},x,o=0;
	cin>>n>>x;
	for(long long i=0;i<n;i++) {
		cin>>a[i];
	}
	for(long long i=0;i<n;i++){
		if(a[i]==x){
			cout<<a[i];
			o++;
		}
	}
	if(o==0){
		cout<<"-1"; 
	}
    return 0;
}
/**************************************************************
	Problem: 1236
	User: panyuchen
	Language: C++
	Result: Wrong Answer
****************************************************************/