What would you expect the runtime of the following code to be

public int fn$($int n$)\{$

if $($n $<=0)$ return $0$ ;

int count $=0$;

for $($int i $=0$ ; i $<$ n ; i$++)$ count$++$;

return count $+$ fn$($n$-2)$;

$\}$

O$(1)$

O$($lg n$)$

O$($n$)$

O$($n lg n$)$

O$($n$^2)$

O$(2^$n$)$