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