#include<bits/stdc++.h>
using namespace std;
int n,m,k=0,l,ans,r=-1,a[10000001];
int main(){
	cin>>n;
	l=n;
	ans=n/2;
	for(int i=0;i<n;i++){
		cin>>a[i];
	}
	cin>>m;
	while(k<l){
		ans=(k+l)/2;
		if(a[ans]==m){
			r=ans;
			break;
		}else if(a[ans]>m){
			l=ans-1;
		}else{
			k=ans+1;
		}
	}
	cout<<r;
	
}
/**************************************************************
	Problem: 1236
	User: zhengzihao
	Language: C++
	Result: Wrong Answer
****************************************************************/