import java.io.PrintStream;
import java.util.Arrays;
import java.util.Scanner;

/**
 * Solution to Water Journal
 * 
 * @author vanb
 */
public class waterjournal_vanb
{
    /** Input. */
    private static Scanner sc;
    
    /** Output. */
    private static PrintStream ps;
    
    /**
     * Do it!
     */
    private void doit()
    {
        int n = sc.nextInt();
        int a = sc.nextInt();
        int b = sc.nextInt();
        
        boolean aSeen = false;
        boolean bSeen = false;
        
        for( int i=0; i<n-1; i++ )
        {
            int w = sc.nextInt();
            if( w==a ) aSeen = true;
            if( w==b ) bSeen = true;
        }
        
        if( aSeen && !bSeen ) ps.println( b );
        else if( bSeen && !aSeen ) ps.println( a );
        else if( !aSeen && !bSeen ) ps.println( -1 );
        else for( int i=a; i<=b; i++ ) ps.println( i );
    }
        
    /**
     * Main.
     * 
     * @param args unused
     * @throws Exception
     */
    public static void main( String[] args ) throws Exception
    {
        sc = new Scanner( System.in );
        ps = System.out;
        
        new waterjournal_vanb().doit();
    }

}