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