You can use the given loop invariant without proof.

$1//$ pre: n $>=1$

$2$ a $3*$n

$3$ sum $0$

$4//$ LoopInv: a is divisible by $3$

$5$ while $($a $>0)$

$6$ b $0$

$7$ while $($b $<$ a$)$

$8$ sum $$ sum $+2*$b

$9$ b $$ b$+1$

$10$ a $$ a$-3$

Calculate the value of the variable sum when the program terminates, as

a function of the input n$.$