#include<bits/stdc++.h> using namespace std; int n,a[10001],s; int find(int l,int r) { int mid=(l+r)/2; while(mid!=l&&a[mid]!=s) { if(a[mid]>s) r=mid; else l=mid+1; mid=(l+r)/2; } if(a[mid]==s) return mid; else return -1; } int main() { cin>>n; for(int i=1;i<=n;i++) cin>>a[i]; cin>>s; cout<<find(1,n); return 0; }