Something

puts "Enter a maximum value:"
max = gets.chomp.to_f

count = 1
number = 0
while number < max
  count += 1
  number = 2 ** count
end

number /= 2
count -= 1

puts "2^" + count.to_s + " = " + number.to_s + " is the highest power of 2 less than " + max.to_s