import java.util.Scanner;
 
public class Main {
    public static void main(String[] args) {
 
        Scanner scanner = new Scanner(System.in);
 
       int N= scanner.nextInt();
       long []arr= new long[N];
 
       for (int i = 0; i < N; i++) {
           arr[i]= scanner.nextLong();
       }
        long X= scanner.nextLong();
        boolean found= false;
 
        for(int i=0;i<N;i++){
           if(X==arr[i]){
               System.out.println(i);
               found=true;
               break;
           }
       }
       if(!found){
           System.out.println(-1);
 
       }
 
        scanner.close();
    }
}
 

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