#include <bits/stdc++.h> using namespace std; int a[10005]; int main(){ int n; cin>>n; for(int i=1;i<=n;i++) cin>>a[i]; int x; cin>>x; int l=1,r=n; while(l<=r){ int mid=(l+r)>>1; if(x==a[mid]) { cout<<mid<<endl; return 0; } else if(x<a[mid]) r=mid-1; else l=mid+1; } cout<<"-1"<<endl; return 0; }