Problem $4.$ Consider the following implementation and test client of a Stack: class Stack:

def

$\_\_$init$\_\_($self$)$: self.$\_$a $=[]$

d e f

pop $($ s e l f $)$ :

val $=$ self.$\_$a $[0]$ self.$\_$a $=$ self.$\_$a $[1$:$]$

return val

# def push $($self$,$ item$)$:

d e f $\_$ ma i n $()$ :

int $($sys$.$ argv $[1])$ s $=$ Stack $()$

for i in range $(1,$ n $+1,2)$: s$.$ push $($i$)$

stdio writeln $($s$.$ pop $()+$ s$.$ pop $())$

if $-\_$name$\_-\_\_$ m a i n $\_\_\text{'}$ : $\_$main $()$