rek     START   0

loop    RD      #0xFA
        COMP    #1
        JLT     halt
        JSUB    fa
        WD      #1
        CLEAR   A
        J       loop

halt    J       halt    

fa      STL     @stkp
        JSUB    spush
        STB     @stkp
        JSUB    spush
        . Base case
        COMP    #2
        JLT     faExit
        RMO     A, B
        SUB     #1
        JSUB    fa
        MULR    B, A


faExit  JSUB   spop
        LDB     @stkp
        JSUB    spop
        LDL     @stkp
        RSUB


sinit   STA     stkA
        LDA     #stk
        STA     stkp
        LDA     stkA
        RSUB

spush   . stkp++
        STA     stkA
        LDA     stkp
        ADD     #3
        STA     stkp
        LDA     stkA
        RSUB

spop    . stkp--
        STA     stkA
        LDA     stkp
        SUB     #3
        STA     stkp
        LDA     stkA
        RSUB

stkp    WORD    0
stk     RESW    1000
stkA    WORD    0 

        END     rek