'''
117 + 4 = 121
'''

from collections import deque

def add(a, b):
	a_i = len(a) -1
	b_i = len(b) - 1
	carry = 0
	ans = deque()
	while a_i >= 0 or b_i >= 0 or carry > 0 :
		sum = 0
		if a_i >= 0:
			sum += int(a[a_i])
		if b_i >= 0:
			sum += int(b[b_i])

		sum += carry

		ans.appendleft(sum%10)
		carry = sum//10
		a_i -= 1
		b_i -=1

	ans_str = ""
	for digit in ans:
		ans_str += str(digit)

	return ans_str



def subtract(a,b):
	# find out if negative
	is_neg = False
	if len(b) > len(a):
		is_neg = True
	if len(a) == len(b):
		for i,digit in enumerate(a):
			if digit < b[i]:
				is_neg = True
				break

	if is_neg:
		a,b = b,a

	a_i = len(a) - 1
	b_i = len(b) - 1
	carry = 0
	ans = deque()
	while a_i >= 0 or b_i >= 0 or carry != 0 :
		diff = 0
		if a_i >= 0:
			diff += carry + int(a[a_i])
		if b_i >= 0:
			if a[a_i] < b[b_i]:
				carry = -1
				diff += 10
			else:
				carry = 0
			diff -= int(b[b_i])

		ans.appendleft(diff)

	ans_str = ""
	if is_neg:
		ans_str += "-"

	if ans[0] == 0:
		leading_0 = True
	for digit in ans:
		if digit == 0 and leading_0:
			continue

		if digit != 0:
			leading_0 = False

		ans_str += str(digit)

	if ans_str == "":
		return "0"

	return ans_str


def add_w_negs(a,b):
	if a[0] == "-" and b[0] == "-":
		ans = add(a[1:], b[1:])
		ans = "-" + ans

	elif a[0] == "-":
		ans = subtract(b, a[1:])

	elif b[0] == "-":
		ans = subtract(a, b[1:])

	else:
		ans = add(a,b)
	return ans

def subtract_w_negs(a,b):
	if a[0] == "-" and b[0] == "-":
		ans = subtract(b[1:], a[1:])

	elif a[0] == "-":
		ans = add(b, a[1:])
		ans = "-" + ans

	elif b[0] == "-":
		ans = add(a, b[1:])

	else:
		ans = subtract(a,b)
	return ans