#include<bits/stdc++.h>
using namespace std;
int a[1000000],n,x,ans=-1;
void ss(int l,int r){
	if(l<=r){
		int mid=(l+r)/2;
		if(a[mid]==x)	ans=mid+1;
		if(a[mid]>x)	ss(l,mid-1);
		if(a[mid]<x)	ss(mid+1,r);
	}
}
int main(){	
	cin>>n;
	for(int i=0;i<n;i++)	cin>>a[i];
	cin>>x;
	ss(0,n-1);
	cout<<ans;
	return 0;
}
/**************************************************************
	Problem: 1236
	User: zzz
	Language: C++
	Result: Accepted
	Time:323 ms
	Memory:5980 kb
****************************************************************/