#include<bits/stdc++.h> using namespace std; int n,x; int a[100001]; int main(){ cin>>n; for(int i=1;i<=n;i++){ cin>>a[i]; } cin>>x; int l=1,r=n,f=0; while(l<=r){ int mid=(l+r)/2; if(a[mid]==x){ cout<<mid; f=1; break; } else if(a[mid]>x) r=mid-1; else l=mid+1; } if(f==0) cout<<-1; return 0; }