include<bits/stdc++.h>

using namespace std; const int N=1e6; int a[N]; int p=-1; int f(int l,int r,int x){

if(l>r)return p;
int mid=l+(r-l)/2;
if(x==a[mid]){
	p=mid;
	return f(l,mid-1,x);
}
if(x<a[mid])return f(l,mid-1,x);
if(x>a[mid])return f(mid+1,r,x);

} int main(){

int n;
cin>>n;
for(int i=1;i<=n;i++){
	cin>>a[i];
}
int x,l=1,r=n;
cin>>x;
f(l,r,x);
cout<<p;

}