What does the following statement sequence print if the user input is $123?$

public static void main$($String$[]$ args$)$

$\{$

Scanner in $=$ new Scanner$($

System.in$)$;

System.out.print$("$Enter a number: $")$;

String str $=$ in$.$next$()$;

str $+=456$;

System.out.println$($str$)$;

$\}$

$579$

Compile$-$time error

$123456$

Run$-$time error