#!/bin/env ruby
#
# given a series of digits, prints the BVR (Swiss Post Bulletin de Versement)
# digit key sum
#

def bvr_sum(string)
    retval = 0
    string.scan(/./) { |char|
        retval = [ 0, 9, 4, 6, 8, 2, 7, 1, 3, 5 ][ (retval + Integer(char)) % 10]
    }
    return (10 - retval) % 10
end

puts "BVR digit key for #{ARGV[0]}: #{bvr_sum(ARGV[0])}"