#include <iostream>
using namespace std;
int main() {
    long long n,a[100000000]={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<<i+1;
    		o++;
    	}
    }
    if(o==0){
    	cout<<"-1";
    }
    return 0;
}
/**************************************************************
	Problem: 1236
	User: panyuchen
	Language: C++
	Result: Runtime Error
****************************************************************/