Valery is a PE teacher at a school in Berland. Soon the students are going to take a test in long jumps, and Valery has lost his favorite ruler! 

However, there is no reason for disappointment, as Valery has found another ruler, its length is l centimeters. The ruler already has n marks, with which he can make measurements. We assume that the marks are numbered from 1 to n in the order they appear from the beginning of the ruler to its end. The first point coincides with the beginning of the ruler and represents the origin. The last mark coincides with the end of the ruler, at distance l from the origin. This ruler can be repesented by an increasing sequence a_1, a_2, ..., a_{n}, where a_{i} denotes the distance of the i-th mark from the origin (a_1 = 0, a_{n} = l).

Valery believes that with a ruler he can measure the distance of d centimeters, if there is a pair of integers i and j (1 ≤ i ≤ j ≤ n), such that the distance between the i-th and the j-th mark is exactly equal to d (in other words, a_{j} - a_{i} = d). 

Under the rules, the girls should be able to jump at least x centimeters, and the boys should be able to jump at least y (x < y) centimeters. To test the children's abilities, Valery needs a ruler to measure each of the distances x and y. 

Your task is to determine what is the minimum number of additional marks you need to add on the ruler so that they can be used to measure the distances x and y. Valery can add the marks at any integer non-negative distance from the origin not exceeding the length of the ruler.


-----Input-----

The first line contains four positive space-separated integers n, l, x, y (2 ≤ n ≤ 10^5, 2 ≤ l ≤ 10^9, 1 ≤ x < y ≤ l) — the number of marks, the length of the ruler and the jump norms for girls and boys, correspondingly.

The second line contains a sequence of n integers a_1, a_2, ..., a_{n} (0 = a_1 < a_2 < ... < a_{n} = l), where a_{i} shows the distance from the i-th mark to the origin.


-----Output-----

In the first line print a single non-negative integer v — the minimum number of marks that you need to add on the ruler.

In the second line print v space-separated integers p_1, p_2, ..., p_{v} (0 ≤ p_{i} ≤ l). Number p_{i} means that the i-th mark should be at the distance of p_{i} centimeters from the origin. Print the marks in any order. If there are multiple solutions, print any of them.


-----Examples-----
Input
3 250 185 230
0 185 250

Output
1
230

Input
4 250 185 230
0 20 185 250

Output
0

Input
2 300 185 230
0 300

Output
2
185 230



-----Note-----

In the first sample it is impossible to initially measure the distance of 230 centimeters. For that it is enough to add a 20 centimeter mark or a 230 centimeter mark.

In the second sample you already can use the ruler to measure the distances of 185 and 230 centimeters, so you don't have to add new marks.

In the third sample the ruler only contains the initial and the final marks. We will need to add two marks to be able to test the children's skills.

Difficulty: MEDIUM_HARD
Tags: Sorting

Implementation

Greedy algorithms
Skill types: Sorting

Greedy algorithms

Starter code:

Solutions:
def solve(n, l, x, y, a):
	s = set()
	(fx, fy, fxy, fyx) = (False, False, False, False)
	vxy = -1
	(vyx_min, vyx_max) = (-1, -1)
	for v in a:
		if v - x in s:
			fx = True
		if v - y in s:
			fy = True
		if v - (x + y) in s:
			fxy = True
			vxy = v
		if v - (y - x) in s:
			if not fyx:
				fyx = True
				vyx_min = vyx_max = v
			else:
				vyx_max = v
		s.add(v)
	if fx and fy:
		print(0)
	elif fx:
		print(1)
		print(y)
	elif fy:
		print(1)
		print(x)
	elif fxy:
		print(1)
		print(vxy - y)
	elif fyx:
		if vyx_min + x < l:
			print(1)
			print(vyx_min + x)
		elif vyx_max - y > 0:
			print(1)
			print(vyx_max - y)
		else:
			print(2)
			print(x, y)
	else:
		print(2)
		print(x, y)
(n, l, x, y) = map(int, input().split())
a = list(map(int, input().split()))
solve(n, l, x, y, a)


import math
import collections
import bisect
import heapq
import time
import random
import itertools
import sys
from typing import List

def solve(N, L, X, Y, A):
	vs = set(A)
	mx = any([a + X in vs for a in A])
	my = any([a + Y in vs for a in A])
	if mx and my:
		print(0)
	elif mx:
		print(1)
		print(Y)
	elif my:
		print(1)
		print(X)
	else:
		for a in vs:
			for (b, c) in [(a + X, Y), (a + Y, X), (a - X, Y), (a - Y, X)]:
				if 0 <= b <= L:
					if b + c <= L and b + c in vs or (b - c >= 0 and b - c in vs):
						print(1)
						print(b)
						return
		print(2)
		print('{} {}'.format(X, Y))
(N, L, X, Y) = map(int, input().split())
A = [int(x) for x in input().split()]
solve(N, L, X, Y, A)


import itertools
import math

def can_measure(a, d):
	return any((i + d in a for i in a))

def main():
	(n, l, x, y) = map(int, input().split())
	a = set(map(int, input().split()))
	can_x = can_measure(a, x)
	can_y = can_measure(a, y)
	if can_x and can_y:
		print(0)
	elif can_x:
		print(1)
		print(y)
	elif can_y:
		print(1)
		print(x)
	else:
		for i in a:
			if i + x + y in a:
				print(1)
				print(i + x)
				break
			else:
				t = i + x - y in a
				if 0 <= i + x <= l and t:
					print(1)
					print(i + x)
					break
				if 0 <= i - y <= l and t:
					print(1)
					print(i - y)
					break
		else:
			print(2)
			print(x, y)

def __starting_point():
	main()
__starting_point()


(n, l, x, y) = list(map(int, input().split(' ')))
li = list(map(int, input().split(' ', n)[:n]))
li.sort()
dic = {}
(a1, a2) = (0, 0)
ans = 2
x1 = x
y1 = y
xi = -1
yi = -1
for i in li:
	dic[i] = 1
for i in range(n):
	if li[i] - x >= 0:
		if li[i] - x in dic:
			a1 = 1
			xi = i
	if li[i] + x <= l:
		if li[i] + x in dic:
			a1 = 1
			xi = i
	if li[i] - y >= 0:
		if li[i] - y in dic:
			a2 = 1
			yi = i
	if li[i] + y <= l:
		if li[i] + y in dic:
			a2 = 1
			yi = i
if a1 == 1 and a2 == 1:
	print(0)
elif a1 == 1:
	if li[xi] - x >= 0:
		if li[xi] - x in dic:
			if li[xi] - x + y <= l and li[xi] - x + y in dic:
				a2 = 1
			if li[xi] - x - y >= 0 and li[xi] - x - y in dic:
				a2 = 1
	if li[xi] + x <= l:
		if li[xi] + x in dic:
			if li[xi] + x + y <= l and li[xi] + x + y in dic:
				a2 = 1
			if li[xi] + x - y >= 0 and li[xi] + x - y in dic:
				a2 = 1
	if a2 == 1:
		print(0)
	else:
		print(1)
		print(y)
elif a2 == 1:
	if li[yi] - y >= 0:
		if li[yi] - y in dic:
			if li[yi] - y + x <= l and li[yi] - y + x in dic:
				a1 = 1
			if li[yi] - y - x >= 0 and li[yi] - y - x in dic:
				a1 = 1
	if li[yi] + y <= l:
		if li[yi] + x in dic:
			if li[yi] + y + x <= l and li[yi] + y + x in dic:
				a1 = 1
			if li[yi] + y - x >= 0 and li[yi] + y - x in dic:
				a1 = 1
	if a1 == 1:
		print(0)
	else:
		print(1)
		print(x)
else:
	for i in range(n):
		if li[i] - x >= 0:
			a1 = 1
			xi = i
			if li[xi] - x + y <= l and li[xi] - x + y in dic:
				a2 = 1
			if li[xi] - x - y >= 0 and li[xi] - x - y in dic:
				a2 = 1
			if a2 == 1:
				print(1)
				print(li[i] - x)
				break
			else:
				a1 = 0
		if li[i] + x <= l:
			a1 = 1
			xi = i
			if li[xi] + x + y <= l and li[xi] + x + y in dic:
				a2 = 1
			if li[xi] + x - y >= 0 and li[xi] + x - y in dic:
				a2 = 1
			if a2 == 1:
				print(1)
				print(li[i] + x)
				break
			else:
				a1 = 0
		if li[i] - y >= 0:
			a2 = 1
			yi = i
			if li[yi] - y + x <= l and li[yi] - y + x in dic:
				a1 = 1
			if li[yi] - y - x >= 0 and li[yi] - y - x in dic:
				a1 = 1
			if a1 == 1:
				print(1)
				print(li[i] - y)
				break
			else:
				a2 = 0
		if li[i] + y <= l:
			a2 = 1
			yi = i
			if li[yi] + y + x <= l and li[yi] + y + x in dic:
				a1 = 1
			if li[yi] + y - x >= 0 and li[yi] + y - x in dic:
				a1 = 1
			if a1 == 1:
				print(1)
				print(li[i] + y)
				break
			else:
				a2 = 0
if a1 == 0 and a2 == 0:
	print(2)
	print(x, y)


import sys
first = sys.stdin.readline().split(' ')
n = int(first[0])
l = int(first[1])
x = int(first[2])
y = int(first[3])
second = sys.stdin.readline().split(' ')
have_dict = {}
need_dict_x = {}
need_dict_y = {}
for val in second:
	have_dict[val] = 1
	val = int(val)
	need_dict_x[str(val - x)] = 1
	need_dict_x[str(val + x)] = 1
	need_dict_y[str(val - y)] = 1
	need_dict_y[str(val + y)] = 1
need_x = 1
need_y = 1
something = 1
for val in have_dict.keys():
	try:
		need_dict_x[val]
		need_x = 0
	except:
		something += 1
	try:
		need_dict_y[val]
		need_y = 0
	except:
		something -= 1
need_vals = []
if need_x == 1 and need_y == 1:
	to_return = 2
	return_val = str(x) + ' ' + str(y)
	for val in need_dict_x.keys():
		if int(val) < 0 or int(val) > l:
			continue
		else:
			try:
				need_dict_y[val]
				to_return = 1
				return_val = val
			except:
				continue
	print(to_return)
	print(return_val)
else:
	print(need_x + need_y)
	if need_x == 1:
		print(x)
	elif need_y == 1:
		print(y)


(n, l, x, y) = map(int, input().split())
s = set(map(int, input().split()))

def f(d):
	return any((i + d in s for i in s))

def g():
	for i in s:
		if i + x + y in s:
			return i + x
	return 0

def h():
	for i in s:
		if i + y - x in s:
			if i - x >= 0:
				return i - x
			if i + y <= l:
				return i + y
	return 0

def e(d):
	print(1)
	print(d)
if f(x):
	if f(y):
		print(0)
	else:
		e(y)
elif f(y):
	e(x)
else:
	z = g()
	if z:
		e(z)
	else:
		z = h()
		if z:
			e(z)
		else:
			print(2)
			print(x, y)


def main():
	import sys
	tokens = [int(i) for i in sys.stdin.read().split()]
	tokens.reverse()
	(n, l, x, y) = [tokens.pop() for i in range(4)]
	marks = set(tokens)
	x_index = y_index = sum_index = sub_index1 = sub_index2 = -1
	for i in marks:
		if i + x in marks:
			x_index = y
		if i + y in marks:
			y_index = x
		if i + x + y in marks:
			sum_index = i + x
		if i + y - x in marks and i - x >= 0:
			sub_index1 = i - x
		if i + y - x in marks and i + y <= l:
			sub_index2 = i + y
	if x_index != -1 and y_index != -1:
		print(0)
	else:
		for i in (x_index, y_index, sum_index, sub_index1, sub_index2):
			if i != -1:
				print(1)
				print(i)
				break
		else:
			print(2)
			print(x, y)
main()


from collections import defaultdict as dc

def serch(a, b, x, y):
	for i in range(1, n):
		if b[a[i] - x - y]:
			return a[i] - y
		if b[a[i] - (y - x)] and a[i] + x <= l:
			return a[i] + x
		if b[a[i] + (y - x)] and a[i] - x >= 0:
			return a[i] - x
	return 0
(n, l, x, y) = [int(i) for i in input().split()]
a = [int(i) for i in input().split()]
b = dc(int)
b = dc(lambda : 0, b)
k1 = 0
k2 = 0
for i in range(n):
	b[a[i]] = 1
	if b[a[i] - x] == 1:
		k1 = 1
	if b[a[i] - y] == 1:
		k2 = 1
if k1 == 1 and k2 == 1:
	print(0)
elif k1 == 0 and k2 == 0:
	z = serch(a, b, x, y)
	if z != 0:
		print(1)
		print(z)
	else:
		print(2)
		print(x, y)
elif k1 == 0:
	print(1)
	print(x)
else:
	print(1)
	print(y)


def main():
	import sys
	tokens = [int(i) for i in sys.stdin.read().split()]
	tokens.reverse()
	(n, l, x, y) = [tokens.pop() for i in range(4)]
	marks = set(tokens)
	flag_x = flag_y = False
	index = -1
	for i in marks:
		if i + x in marks:
			flag_x = True
			index = y
		if i + y in marks:
			flag_y = True
			index = x
		if i + x + y in marks:
			index = i + x
		if i + y - x in marks and i - x >= 0:
			index = i - x
		if i + y - x in marks and i + y <= l:
			index = i + y
	if flag_x and flag_y:
		print(0)
	elif index != -1:
		print(1)
		print(index)
	else:
		print(2)
		print(x, y)
main()


from collections import defaultdict
(n, l, x, y) = map(int, input().split())
arr = [int(x) for x in input().split()]
d = defaultdict(bool)
for i in arr:
	d[i] = True
xs = False
ys = False
for (i, v) in enumerate(arr):
	if d[v + x] or d[v - x]:
		xs = True
	if d[v - y] or d[v + y]:
		ys = True
if xs and ys:
	print(0)
elif xs:
	print(1)
	print(y)
elif ys:
	print(1)
	print(x)
else:
	done = False
	(a1, a2) = (0, 0)
	for (i, v) in enumerate(arr):
		plusY = v + y
		if 0 <= plusY <= l:
			if d[plusY - x]:
				(a1, a2) = (plusY, plusY - x)
				done = True
				break
			if d[plusY + x]:
				(a1, a2) = (plusY, plusY + x)
				done = True
				break
		negY = v - y
		if 0 <= negY <= l:
			if d[negY - x]:
				(a1, a2) = (negY, negY - x)
				done = True
				break
			if d[negY + x]:
				(a1, a2) = (negY, negY + x)
				done = True
				break
		plusX = v + x
		if 0 <= plusX <= l:
			if d[plusX - y]:
				(a1, a2) = (plusX, plusX - y)
				done = True
				break
			if d[plusX + y]:
				(a1, a2) = (plusX, plusX + y)
				done = True
				break
		negX = v - x
		if 0 <= negX <= l:
			if d[negX - y]:
				(a1, a2) = (negX, negX - y)
				done = True
				break
			if d[negX + y]:
				(a1, a2) = (negX, negX + y)
				done = True
				break
	if done:
		print(1)
		print(a1)
	else:
		print(2)
		print(x, y)


R = lambda : map(int, input().split())
(n, l, x, y) = R()
arr = set(R())
(x_good, y_good) = (False, False)
for m in arr:
	if m + x in arr or m - x in arr:
		x_good = True
		break
for m in arr:
	if m + y in arr or m - y in arr:
		y_good = True
		break
if x_good and y_good:
	print(0)
	return
elif x_good:
	print(1)
	print(y)
	return
elif y_good:
	print(1)
	print(x)
	return
else:
	for m in arr:
		if m + x <= l and (m + x + y in arr or m + x - y in arr):
			print(1)
			print(m + x)
			return
		if m - x >= 0 and (m - x + y in arr or m - x - y in arr):
			print(1)
			print(m - x)
			return
		if m + y <= l and (m + y + x in arr or m + y - x in arr):
			print(1)
			print(m + y)
			return
		if m - y >= 0 and (m - y + x in arr or m - y - x in arr):
			print(1)
			print(m - y)
			return
print(2)
print(x, y)


a = input().split(' ')
b = input().split(' ')
n = int(a[1])
x = int(a[2])
y = int(a[3])
xcan = False
ycan = False
xycan = False
xymoar = False
cool = 0
cool2 = 0
s = set()
for element in b:
	s.add(int(element))
for c in s:
	if c + x in s:
		xcan = True
	if c + y in s:
		ycan = True
	if c + x + y in s:
		xycan = True
		cool = c
	if c + y - x in s:
		if c + y > n:
			if c - x < 0:
				pass
			else:
				cool2 = c - x
				xymoar = True
		else:
			xymoar = True
			cool2 = c + y
	if xcan:
		if ycan:
			break
if xcan == True:
	if ycan == True:
		result = 0
		marks = []
	else:
		result = 1
		marks = [y]
elif ycan == True:
	result = 1
	marks = [x]
elif xycan == True:
	result = 1
	marks = [cool + x]
elif xymoar == True:
	result = 1
	marks = [cool2]
else:
	result = 2
	marks = [x, y]
print(result)
for i in range(len(marks)):
	print(marks[i], end=' ')


def main():
	from bisect import bisect_left
	(n, l, x, y) = map(int, input().split())
	(aa, d) = (list(map(int, input().split())), {})
	for z in (x, y, y + x):
		for a in aa:
			a += z
			if a > l:
				break
			b = aa[bisect_left(aa, a)]
			if b <= a:
				if b == a:
					d[z] = a
				break
		if len(d) == 2:
			break
	if d:
		if x in d and y in d:
			res = []
		elif x in d:
			res = [y]
		elif y in d:
			res = [x]
		elif y + x in d:
			res = [d[y + x] - y]
	else:
		(z, tmp) = (y - x, [])
		for a in aa:
			a += z
			if a > l:
				break
			b = aa[bisect_left(aa, a)]
			if b == a:
				tmp.append(a)
		for a in tmp:
			if a > y:
				res = [a - y]
				break
			elif a + x < l:
				res = [a + x]
				break
		else:
			res = [x, y]
	print(len(res))
	if res:
		print(*res)
main()


(n, l, x, y) = list(map(int, input().split()))
a = set(map(int, input().split()))
ok1 = ok2 = ok3 = False
for c in a:
	if c + x in a:
		ok1 = True
	if c + y in a:
		ok2 = True
	if c - x > 0 and c - x + y in a:
		ok3 = True
		mark = c - x
	if c + x < l and c + x - y in a:
		ok3 = True
		mark = c + x
	if c + x + y in a:
		ok3 = True
		mark = c + x
	if c - x - y in a:
		ok3 = True
		mark = c - x
if ok1 and ok2:
	print(0)
elif not ok1 and (not ok2):
	if ok3:
		print(1)
		print(mark)
	else:
		print(2)
		print(x, y)
else:
	print(1)
	print(y if ok1 else x)


def rl(T=str):
	return list(map(T, input().split()))

def ok(a, d, x):
	for v in a:
		if v + x in d:
			return True
	return False

def try_one(a, d, x, y):

	def can_place(v):
		if a[0] <= v <= a[-1]:
			if (v + x in d or v - x in d) and (v + y in d or v - y in d):
				return True
		return False
	for v in a:
		for _ in [-x, +x, -y, +y]:
			if can_place(v + _):
				return v + _
	return None

def main():
	(n, l, x, y) = rl(int)
	a = rl(int)
	d = set(a)
	if ok(a, d, x):
		if ok(a, d, y):
			print(0)
		else:
			print(1)
			print(y)
	elif ok(a, d, y):
		print(1)
		print(x)
	else:
		p = try_one(a, d, x, y)
		if p is not None:
			print(1)
			print(p)
		else:
			print(2)
			print(x, y)
main()


(n, l, x, y) = list(map(int, input().split()))
a = set(map(int, input().split()))
boy = False
girl = False
one = False
where = -1
for i in a:
	if i + x in a:
		boy = True
	if i + y in a:
		girl = True
	if i - x > 0 and i - x + y in a:
		one = True
		where = i - x
	if i + x < l and i + x - y in a:
		one = True
		where = i + x
	if i + x + y in a:
		one = True
		where = i + x
	if i - x - y in a:
		one = True
		where = i - x
if boy and girl:
	print(0)
if boy and (not girl):
	print(1)
	print(y)
if girl and (not boy):
	print(1)
	print(x)
if not boy and (not girl):
	if one:
		print(1)
		print(where)
	if not one:
		print(2)
		print(x, y)


(n, l, x, y) = map(int, input().split())
a = list(map(int, input().split()))
i = 0
j = 1
tot = 0
can_measure_a = False
while j < n:
	if a[j] - a[i] == x:
		can_measure_a = True
		break
	elif a[j] - a[i] > x:
		i += 1
	else:
		j += 1
i = 0
j = 1
can_measure_b = False
while j < n:
	if a[j] - a[i] == y:
		can_measure_b = True
		break
	elif a[j] - a[i] > y:
		i += 1
	else:
		j += 1
if can_measure_a and can_measure_b:
	print(0)
elif can_measure_a:
	print(1)
	print(y)
elif can_measure_b:
	print(1)
	print(x)
else:
	a = set(a)
	for el in a:
		if el + x + y in a:
			print(1)
			print(el + x)
			break
		else:
			t = el + x - y in a
			if 0 <= el + x <= l and t:
				print(1)
				print(el + x)
				break
			if 0 <= el - y <= l and t:
				print(1)
				print(el - y)
				break
	else:
		print(2)
		print(x, y)


__author__ = 'zabidon'
(n, l, x, y) = map(int, input().split())
data = set(map(int, input().split()))
old_x = any((i + x in data for i in data))
old_y = any((i + y in data for i in data))
if old_x and old_y:
	print(0)
elif old_x:
	print(1)
	print(y)
elif old_y:
	print(1)
	print(x)
else:
	found = False
	for i in data:
		if i + x + y in data:
			found = True
			print(1)
			print(i + x)
		elif i + x - y in data:
			if 0 <= i + x <= l:
				found = True
				print(1)
				print(i + x)
			if not found and 0 <= i - y <= l:
				found = True
				print(1)
				print(i - y)
		if found:
			break
	if not found:
		print(2)
		print(x, y)


def fastio():
	import sys
	from io import StringIO
	from atexit import register
	global input
	sys.stdin = StringIO(sys.stdin.read())
	input = lambda : sys.stdin.readline().rstrip('\r\n')
	sys.stdout = StringIO()
	register(lambda : sys.__stdout__.write(sys.stdout.getvalue()))
fastio()
MOD = 10 ** 9 + 7
I = lambda : list(map(int, input().split()))
(n, l, x, y) = I()
a = I()
s = set(a)
f = 0
for i in range(n):
	if a[i] + x in s:
		break
else:
	f = 1
for i in range(n):
	if a[i] + y in s:
		break
else:
	f += 2
if f == 1:
	print(1)
	print(x)
elif f == 2:
	print(1)
	print(y)
elif f == 0:
	print(0)
else:
	for i in range(n):
		k = a[i] + x
		if 0 <= k <= l and (k - y >= 0 and k - y in s or (k + y <= l and k + y in s)):
			print(1)
			print(k)
			exit()
		k = a[i] - x
		if 0 <= k <= l and (k - y >= 0 and k - y in s or (k + y <= l and k + y in s)):
			print(1)
			print(k)
			exit()
	for i in range(n):
		k = a[i] + y
		if 0 <= k <= l and (k - x >= 0 and k - x in s or (k + x <= l and k + x in s)):
			print(1)
			print(k)
			break
		k = a[i] - y
		if 0 <= k <= l and (k - x >= 0 and k - x in s or (k + x <= l and k + x in s)):
			print(1)
			print(k)
			break
	else:
		print(2)
		print(x, y)


(n, l, x, y) = list(map(int, input().split()))
v = list(map(int, input().split()))
s = set(v)
cx = 0
for i in range(n):
	if v[i] + x in s:
		cx = 1
		break
cy = 0
for i in range(n):
	if v[i] + y in s:
		cy = 1
		break
count = 0
ans = []
if cx == 0:
	count += 1
	ans.append(x)
if cy == 0:
	count += 1
	ans.append(y)
if count == 2:
	for i in range(n):
		if v[i] + x + y in s:
			count = 1
			ans = [v[i] + x]
			break
if count == 2:
	for i in range(n):
		if v[i] + x - y in s:
			if v[i] + x <= l:
				count = 1
				ans = [v[i] + x]
				break
			elif v[i] - y >= 0:
				count = 1
				ans = [v[i] - y]
				break
print(count)
if count != 0:
	print(*ans)


from collections import defaultdict

class LongJumps:

	def __init__(self, n, l, x, y, a):
		(self.n, self.l, self.x, self.y, self.a) = (n, l, x, y, a)

	def get_markers(self):
		st = defaultdict(set)
		req_pts = [self.x, self.y]
		exist_check = defaultdict(bool)
		value_check = defaultdict(bool)
		for v in self.a:
			exist_check[v] = True
		for v in self.a:
			for i in range(len(req_pts)):
				if v - req_pts[i] >= 0:
					st[v - req_pts[i]].add(i)
					if exist_check[v - req_pts[i]]:
						value_check[i] = True
				if v + req_pts[i] <= l:
					st[v + req_pts[i]].add(i)
					if exist_check[v + req_pts[i]]:
						value_check[i] = True
		if value_check[0] and value_check[1]:
			print(0)
			return
		sol_status = 2
		status1_marker = None
		for v in st:
			if len(st[v]) == 2:
				sol_status = 1
				status1_marker = v
			elif len(st[v]) == 1:
				if exist_check[v]:
					sol_status = 1
					status1_marker = req_pts[1 - st[v].pop()]
		if sol_status == 1:
			print(1)
			print(status1_marker)
			return
		else:
			print(2)
			print(x, y)
(n, l, x, y) = list(map(int, input().strip(' ').split(' ')))
a = list(map(int, input().strip(' ').split(' ')))
lj = LongJumps(n, l, x, y, a)
lj.get_markers()


def main():
	(n, l, x, y) = list(map(int, input().split()))
	arr = set(map(int, input().split()))
	first = False
	second = False
	for i in arr:
		if i + x in arr:
			first = True
		if i + y in arr:
			second = True
	if first and (not second):
		print(1)
		print(y)
		return
	if second and (not first):
		print(1)
		print(x)
		return
	if first and second:
		print(0)
		return
	found = False
	for i in arr:
		if i + x - y in arr and i + x <= l:
			found = True
			coord = i + x
			break
		if i + y - x in arr and i + y <= l:
			found = True
			coord = i + y
			break
		if i + x + y in arr and i + min(x, y) <= l:
			found = True
			coord = i + min(x, y)
		if i - x - y in arr and i - max(x, y) >= 0:
			found = True
			coord = i - max(x, y)
		if i - x + y in arr and i - x >= 0:
			found = True
			coord = i - x
			break
		if i - y + x in arr and i - y >= 0:
			found = True
			coord = i - y
			break
		if found:
			break
	if found:
		print(1)
		print(coord)
		return
	print(2)
	print(x, y)
main()


(n, l, x, y) = map(int, input().split())

def f(t, q):
	i = j = 0
	while j < n:
		d = t[j] - t[i]
		if d < q:
			j += 1
		elif d > q:
			i += 1
		else:
			return 0
	return q

def g(t):
	q = x + y
	i = j = 0
	while j < n:
		d = t[j] - t[i]
		if d < q:
			j += 1
		elif d > q:
			i += 1
		else:
			return t[j]
	return 0

def h(t):
	q = y - x
	i = j = 0
	while j < n:
		d = t[j] - t[i]
		if d < q:
			j += 1
		elif d > q:
			i += 1
		else:
			(a, b) = (t[i] - x, t[j] + x)
			if a >= 0:
				return [a]
			if b <= l:
				return [b]
			j += 1
	return [x, y]

def e(t):
	print(len(t))
	print(' '.join(map(str, t)))
t = list(map(int, input().split()))
t.sort()
x = f(t, x)
y = f(t, y)
if x and y:
	z = g(t)
	if z:
		e([z - y])
	else:
		e(h(t))
elif x:
	e([x])
elif y:
	e([y])
else:
	e([])