longmul

@echo off
setlocal EnableDelayedExpansion
set Number1=%1
set Number2=%2
set /A length1=0
set /A length2=0
:l1
    set /A length1=%length1%+1
    if NOT "!Number1:~%length1%,1!" == "" goto :l1
:l2
    set /A length2=%length2%+1
    if NOT "!Number2:~%length2%,1!" == "" goto :l2
set curn2=0 rem текущая цифра из 2 числа
set ans=0
set remainder=0
set curzerro=0
set /A length2=%length2%-1

set curn2=!Number2:~%length2%,1!
set /A curlength1=!length1!-1
set /A curm=!Number1:~%curlength1%,1!*!curn2!
set /A curm=!curm!+%remainder%
if %curm% LSS 10 (
    set curans=%curm%
    set /A remainder=0
) else (
    set curans=%curm:~1,1%
    set /A remainder=%curm:~0,1%
)
set /A curlength1=!curlength1!-1
if %curlength1% LSS 0 goto :q

:m
    set /A curm=!Number1:~%curlength1%,1!*!curn2!
    set /A curm=!curm!+%remainder%
    if %curm% LSS 10 (
        set curans=%curm%%curans%
        set /A remainder=0
    ) else (
        set curans=%curm:~1,1%%curans%
        set /A remainder=%curm:~0,1%
    )
    set /A curlength1=!curlength1!-1
    if not %curlength1% LSS 0 goto :m
:q
if %remainder% GTR 0 (
    set curans=%remainder%%curans%
    set /A remainder=0
)
set ans=%curans%
set /A length2=%length2%-1
if %length2% LSS 0 goto :qw


:start
    set curn2=!Number2:~%length2%,1!
    set /A curlength1=!length1!-1
    set /A curm=!Number1:~%curlength1%,1!*!curn2!
    set /A curm=!curm!+%remainder%
    if %curm% LSS 10 (
        set curans=%curm%
        set /A remainder=0
    ) else (
        set curans=%curm:~1,1%
        set /A remainder=%curm:~0,1%
    )
    set /A curlength1=!curlength1!-1
    if %curlength1% LSS 0 goto :q1
    :m1
        set /A curm=!Number1:~%curlength1%,1!*!curn2!
        set /A curm=!curm!+%remainder%
        if %curm% LSS 10 (
            set curans=%curm%%curans%
            set /A remainder=0
        ) else (
            set curans=%curm:~1,1%%curans%
            set /A remainder=%curm:~0,1%
        )
        set /A curlength1=!curlength1!-1
        if not %curlength1% LSS 0 goto :m1
    :q1
    set curans=%curans%%curzerro%
    if %remainder% GTR 0 (
        set curans=%remainder%%curans%
        set /A remainder=0
    )
    set curzerro=%curzerro%0
    call sum.cmd %curans% %ans%
    set /A length2=%length2%-1
    if not %length2% LSS 0 goto :start
:qw
echo %ans%
endlocal