#include <bits/stdc++.h> using namespace std; int a[100000860],n,x,l,r,mid,ans=-1; int main(){ cin>>n; for(int i=1;i<=n;i++){ cin>>a[i]; } cin>>x; l=1,r=n; while(l<=r){ mid=(l+r)/2; if(a[mid]==x){ ans=mid; break; }else if(a[mid]>x){ r=mid-1; }else if(a[mid]<x){ l=mid+1; } } cout<<ans; return 0; }