What is the output?

Show your work using paper and pen to trace the output

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

$\{$

char$[]$ input $=$

$\{$

$\}$;

$\text{'}4\text{'},\text{'}6\text{'},\text{'}8\text{'}$

char$[]$ output $=$ new char$[$input$.$length$]$;

f$5($input$,$ output, input.length, $0,0)$;

$\}$

public static void f$5($char$[]$ input, char$[]$ output,

int len, int depth, int start$)$

$\{$

for $($int i $=$ start; i $$ len; i$++)$

$\{$

output$[$depth$]=$ input$[$i$]$;

$\}$

f$5($input$,$ output, len, depth $+1,$ i $+1)$;

if $($depth $==0$ && start $==0)$

$\{$

System.out.println$($

String.valueOf$($output$))$;

$\}$

$\}$