//	l	r	a[m]?x	执行 
//1	1	5	==		ans=3	<-
//2	1	2	<		->
//3	2	2	<		->
//4	2	1	结束 
#include<bits/stdc++.h>
using namespace std;
int n,x,a[100001],ans=-1; 
void ss(int l,int r){
	int m=(l+r)>>1;
	if(a[m]==x){
		ans=m;
		return;
	}
	else if(a[m]<x) ss(m+1,r);
	else ss(l,m-1);
}
int main(){
	scanf("%d",&n);
	for(int i=1;i<=n;i++) scanf("%d",&a[i]);
	scanf("%d",&x);
	ss(1,n);
	printf("%d",ans);
return 0;}

/**************************************************************
	Problem: 1236
	User: fzy001
	Language: C++
	Result: Time Limit Exceed
****************************************************************/