import java.util.*;
public class main{
    public static void main(String[]args){
        Scanner diva = new Scanner(System.in);
        
        int n = diva.nextInt();
        
        if(n<0){
            System.out.print("Invalid input");
            return;
        }
        
        int arr[] = new int[n];
        
        for(int i=0;i<n;i++){
            
             if(!diva.hasNextInt()){
                System.out.print("Invalid input");
                return;
            }
            arr[i] = diva.nextInt();
            
        }
        
    
        int cnt = 0;
        for(int i=0;i<n;i++){
            for(int j=i+1;j<n;j++){       
            if(arr[i]==arr[j]){
                
                cnt++;
            }
          }
        }
          
        if(cnt==0){
            System.out.print("-1");
            return;
        }
        System.out.print(arr[i]);
    }
}