#include<bits/stdc++.h>
using namespace std;
int x,i,n;
long a[100009];
int r,mid,l,ri;
int main(){
cin>>n;
for(i=0;i<n;i++){
	cin>>a[i];
}
cin>>x;
l=0;
ri=n-1;
r=-1;
while(l<=ri){
	mid=(l+ri)/2;
	if(a[mid]==x){
		r=mid;
		break;
	}else if(x<a[mid]){
		ri=mid-1;
	}else if(x>a[mid]){
		l=mid-1;
	}
}
cout<<(r==-1?-1:r+1);
	return 0;
}

/**************************************************************
	Problem: 1589
	User: chenyubo
	Language: C++
	Result: Time Limit Exceed
****************************************************************/