#include<bits/stdc++.h> using namespace std; int a[1000860]; int main(){ int n,ans=-1,x,left,right,mid; cin>>n; for(int i=1;i<=n;i++){ cin>>a[i]; } cin>>x; left=1; right=n; while(left<=right){ mid=(left+right)/2; if(a[mid]==x){ ans=mid; break; }else if(a[mid]>x){ right=mid-1; }else if(a[mid]<x){ left=mid+1; } }cout<<ans; return 0; }