def sqrt_enum(n)
  return to_enum(:sqrt_enum,n) unless block_given?
  list=[]
  while n>0
    list << n%100
    n/=100
  end
  list.reverse
  carry=0
  subcarry=0
  while list[0]||carry!=0
    n=(list.shift||0)+carry*100
    a=(1..10).find{|i|(subcarry*10+i)*i>n}-1
    yield a
    carry=n-(subcarry*10+a)*a
    subcarry=subcarry*10+a*2
  end
end

x=gets.chomp.chars.map(&:to_i)
p sqrt_enum(2).each_cons(3).find_index(x)