#include<bits/stdc++.h> using namespace std; int n,a[10002],m; int main(){ cin>>n; for(int i=1;i<=n;i++) cin>>a[i]; cin>>m; int y=lower_bound(a+1,a+n+1,m)-a; if(y>n||a[y]!=m) cout<<-1; else cout<<y; return 0; }