#include<bits/stdc++.h>
int n,a[1000005],x,ans = -1;
using namespace std;
void m(int l,int r)
{
	int mid = (l + r)>>1;
	if(a[mid]==x){
		ans = mid;
		return;
	}
	else if(a[mid] < x){
		m(mid+1,r);
	}
	else if(a[mid] > x)
	{
		m(l,mid - 1);
	}
}
int main()
{
	cin >> n;
	for(int i = 0; i < n; i++) scanf("&d",a[i]);
	cin >> x;
	m(1,n); 
	cout << ans;
	return 0;
}
/**************************************************************
	Problem: 1236
	User: yangwanning
	Language: C++
	Result: Time Limit Exceed
****************************************************************/