public static int f$1($int n$)$

$\{$

if $($n $<0)$

$\{$

return $0$;

$\}$

else

$\{$

return $($f$1($n $-1)+$ n $*10)$;

$\}$

$\}$

public static int f$2($int n$)$

$\{$

int answer $=0$;

while $($n $>0)$

$\{$

answer $=$ answer $+$ n $*10$;

n$--$;

$\}$

return answer;

$\}$

The method f$2$ will always produce the same results as f$1$ under which of the following conditions?