lib C
  fun strtoll(s : UInt8*, p : UInt8**, b : Int32) : Int64
end

class String
  def to_i64
    C.strtoll(self, nil, 10)
  end
end

s = (read_line.reverse + '0').chars
n = s.size
ans = 0
(0...n).each do |i|
  if s[i] == '1'
    if (s[i + 1]? || '0') == '0'
      s[i] = '0'
    else
      while s[i] == '1'
        s[i] = '0'
        i += 1
      end
      s[i] = '1'
    end
    ans += 1
  end
end
puts ans