class Number:
	def __init__(self, x):
		self.val = x

	def __add__(self, other):
		return Number(self.val+other.val)


class String:
	def __init__(self, s):
		self.val = s

	@staticmethod
	def fromCharCode(x):
		return String(chr(x.val))

	def __add__(self, other):
		return String(self.val+other.val)

	def charAt(self, i=None):
		i = (i or Number(0)).val

		if 0 <= i < len(self.val):
			return String(self.val[i])
		else:
			return String("")

	def substr(self, start=None, length=None):
		start = (start or Number(0)).val
		length = length.val if length is not None else len(self.val)

		if length < 0:
			return String("")

		return String(self.val[start:start+length])

	def slice(self, start=None, end=None):
		start = (start or Number(0)).val
		end = end.val if end is not None else None
		return String(self.val[start:end])


lib = {
	"String": String,
	"document": {"write": lambda x: print(x.val)}
}