#include<bits/stdc++.h>
using namespace std;
int a[1000000],n,x,ans=-1;
void f(int l,int r){
    if(l<=r){
        int mid=(l+r)/2;
        if(a[mid]==x)   ans=mid+1;
        if(a[mid]>x) f(l,mid-1);
        if(a[mid]<x) f(mid+1,r);
    }
}
int main(){ 
    cin>>n;
    for(int i=0;i<n;i++) cin>>a[i];
    cin>>x;
    f(0,n-1);
    cout<<ans;
    return 0;
}
/**************************************************************
	Problem: 1236
	User: linzihang
	Language: C++
	Result: Accepted
	Time:313 ms
	Memory:5980 kb
****************************************************************/