=begin

n! means n × (n − 1) × ... × 3 × 2 × 1

Find the sum of the digits in the number 100!

=end

num = 100

tot = 1
num.downto 2 do |n|
  tot *= n
end

sum = 0
(tot.to_s.length-1).downto 0 do |digitnum|
  sum += tot.to_s[digitnum,1].to_i
end

print(sum)