a = gets.chomp.to_i

(2..10**12).each do |n|
	  num = []
    # lは1ずつ減っていく役
    l = n
    #1周でnumに入る数字を格納
    (1..n-1).each do |m|
		num << m*l
        l = l-1
    end
  	if num.include?(a)
      puts n-1
      break
    end
end
