AtCoder ABC #008

abc008-a.rb

s, t = gets.chomp.split(" ").map(&:to_i)
puts t - s + 1

abc008-b.rb

n = gets.chomp.to_i
res = {}
n.times do
  name = gets.chomp
  if res.key?(name) then
    res[name] += 1
  else
    res[name] = 1
  end
end
puts res.key(res.values.max)

abc008-c.rb

n = gets.chomp.to_i
cc = readlines.map(&:to_i)

res = 0.0
cc.each do |c|
  k = 0
  cc.each do |f|
    k += 1 if c % f == 0
  end
  if k.even? then
    res += (k / 2.0) / k
  else
    res += ((k + 1) / 2.0) / k
  end
end
puts res