fun check(code):
if len of code do not equal to 13
then return false

sum = 0

for i from 1 to 12:
if i is odd:
add code[i] to sum
else:
add code[i] * 3 to sum

checksum = (10 - (sum mod 10)) mod 10

if checksum equals code[13]:
return true
else:
return false