#include<bits/stdc++.h>
using namespace std;
int n,a[1000001]={0},x,r;
int main(){
	int mid,i,left,right;
	cin>>n;
	for(i=0;i<n;i++){
		cin>>a[i];
	}
	cin>>x;
	left=0;
	right=n-1;
	r=-1;
	while(left<=right){
		mid=(left+right)/2;
		if(a[mid]==x){
			r=mid;
			break;
		}
		else if(x<a[mid]){
			right=mid-1;
		}
		else if(x>a[mid]){
			left=mid+1;
		}
	}
	cout<<(r==-1?-1:r+1)<<endl;
	return 0;
}

/**************************************************************
	Problem: 1236
	User: linyifan
	Language: C++
	Result: Accepted
	Time:298 ms
	Memory:5980 kb
****************************************************************/