#include<iostream>
using namespace std;
int main(){
	int a[100]={0},n,i,b;
	cin>>n;
	for(i=0;i<n;i++){
		cin>>a[i];
	}
	cin>>b;
	for(i=0;n-1>i;i++){
		if(a[i]==b){
			i++; 
			cout<<i;
		}
	}cout<<"-1";
}
/**************************************************************
	Problem: 1154
	User: panyuchen
	Language: C++
	Result: Wrong Answer
****************************************************************/