Little Susie loves strings. Today she calculates distances between them. As Susie is a small girl after all, her strings contain only digits zero and one. She uses the definition of Hamming distance:

We will define the distance between two strings s and t of the same length consisting of digits zero and one as the number of positions i, such that s_{i} isn't equal to t_{i}. 

As besides everything else Susie loves symmetry, she wants to find for two strings s and t of length n such string p of length n, that the distance from p to s was equal to the distance from p to t.

It's time for Susie to go to bed, help her find such string p or state that it is impossible.


-----Input-----

The first line contains string s of length n. 

The second line contains string t of length n.

The length of string n is within range from 1 to 10^5. It is guaranteed that both strings contain only digits zero and one.


-----Output-----

Print a string of length n, consisting of digits zero and one, that meets the problem statement. If no such string exist, print on a single line "impossible" (without the quotes).

If there are multiple possible answers, print any of them.


-----Examples-----
Input
0001
1011

Output
0011

Input
000
111

Output
impossible



-----Note-----

In the first sample different answers are possible, namely — 0010, 0011, 0110, 0111, 1000, 1001, 1100, 1101.

Difficulty: EASY

Solutions:
def main():
	(l, f) = ([], True)
	for (a, b) in zip(input(), input()):
		if a == b:
			l.append(a)
		elif f:
			l.append(a)
			f = False
		else:
			l.append(b)
			f = True
	print(''.join(l if f else 'impossible'))
main()


first = input()
second = input()
index = 0
fark = 0
str = ''
while index <= len(first) - 1:
	if first[index] != second[index]:
		fark += 1
		if fark % 2 == 0:
			str += second[index]
		else:
			str += first[index]
	else:
		str += first[index]
	index += 1
if fark % 2 == 0:
	print(str)
else:
	print('impossible')


g = input()
h = input()
c = 0
x = []
for i in range(len(g)):
	if int(g[i]) ^ int(h[i]) == 1:
		if c % 2 == 0:
			x += [g[i]]
		else:
			x += [h[i]]
		c += 1
	else:
		x += [g[i]]
if c % 2 == 0:
	for i in x:
		print(i, end='')
else:
	print('impossible')


s = input()
t = input()
is_impossible = False
res = []
count = 0
for i in range(len(s)):
	if s[i] != t[i]:
		count += 1
		if count % 2 == 1:
			is_impossible = True
			res.append(s[i])
		else:
			is_impossible = False
			res.append(t[i])
	else:
		res.append(t[i])
if is_impossible:
	print('impossible')
else:
	print(''.join(res))


s = input()
t = input()
diffcnt = 0
for (i, j) in zip(s, t):
	if i != j:
		diffcnt += 1
if diffcnt % 2 == 1:
	print('impossible')
	return
cnt = 0
ans = []
for (i, j) in zip(s, t):
	if i == j:
		ans.append(i)
	else:
		ans.append(i if cnt % 2 == 0 else j)
		cnt += 1
print(''.join(ans))


s = str(input())
t = str(input())
ans = ''
flag = 1
c = 0
for i in range(len(s)):
	if s[i] != t[i]:
		c += 1
		if flag:
			ans += s[i]
		else:
			ans += t[i]
		flag = 1 - flag
	else:
		ans += s[i]
print('impossible' if c & 1 else ans)


s = input()
t = input()
e = 0
count_1 = 0
count_2 = 0
s1 = ''
for i in range(len(s)):
	if s[i] == t[i]:
		s1 = s1 + s[i]
	else:
		if e == 0:
			s1 = s1 + s[i]
			count_1 = count_1 + 1
		else:
			s1 = s1 + t[i]
			count_2 = count_2 + 1
		e = 1 - e % 2
if count_1 == count_2:
	print(s1)
else:
	print('impossible')


current = 0
answer = []
s = [x for x in input()]
t = [x for x in input()]
for (x, y) in zip(s, t):
	if x != y:
		answer.append([x, y][current])
		current = 1 - current
	else:
		answer.append(x)
print('impossible' if current else ''.join(answer))


S = input()
T = input()
P = ''
c = 0
A = [0] * len(S)
for i in range(len(S)):
	if S[i] != T[i]:
		c = c + 1
		A[i] = 1
if c % 2 == 0:
	for i in range(len(S)):
		if A[i] == 1:
			c = c - 1
			if c % 2 == 0:
				P = P + T[i]
			else:
				P = P + S[i]
		else:
			P = P + S[i]
	print(P)
else:
	print('impossible')


import sys
s = input()
t = input()
count = 0
for i in range(len(s)):
	if s[i] != t[i]:
		count += 1
if count % 2 == 1:
	print('impossible')
else:
	k = 1
	for i in range(len(s)):
		if s[i] != t[i]:
			if k == 1:
				sys.stdout.write(s[i])
				k = 2
			else:
				sys.stdout.write(t[i])
				k = 1
		else:
			sys.stdout.write(s[i])


s = input()
t = input()
count = 0
for i in range(len(s)):
	if s[i] != t[i]:
		count += 1
if count % 2 != 0:
	print('impossible')
else:
	count = 0
	for i in range(len(s)):
		if s[i] != t[i]:
			if count % 2 == 0:
				print(s[i], end='')
			else:
				print(t[i], end='')
			count += 1
		else:
			print(s[i], end='')


s = input()
t = input()
n = len(s)
l = []
dist = 0
for i in range(n):
	if s[i] != t[i]:
		dist += 1
if dist % 2:
	print('impossible')
else:
	flag = 0
	for i in range(n):
		if s[i] == t[i]:
			l.append(s[i])
		elif flag == 0:
			l.append(s[i])
			flag = 1
		else:
			l.append(t[i])
			flag = 0
	print(''.join(l))


s = input()
t = input()
n = len(s)
dist = 0
for i in range(n):
	if s[i] != t[i]:
		dist += 1
if dist % 2 == 1:
	print('impossible')
else:
	p = ''
	flag = 0
	for i in range(n):
		if s[i] != t[i] and flag == 0:
			p += s[i]
			flag = flag ^ 1
		elif s[i] != t[i] and flag == 1:
			p += t[i]
			flag = flag ^ 1
		elif s[i] == t[i]:
			p += s[i]
	print(p)


s1 = str(input())
t1 = str(input())
s = [int(i) for i in s1]
t = [int(i) for i in t1]
n = len(s)
j = 0
l = []
for i in range(n):
	if s[i] == t[i]:
		l.append(s[i])
	elif j == 0:
		l.append(s[i])
		j = 1
	else:
		l.append(t[i])
		j = 0
if j == 0:
	p = ''
	for i in l:
		p += str(i)
	print(p)
else:
	print('impossible')


s1 = input()
s2 = input()
cnt = 0
s = ''
for i in range(len(s1)):
	if s1[i] != s2[i]:
		if cnt % 2 == 0:
			s += s1[i]
		else:
			s += s2[i]
		cnt += 1
	else:
		s += s1[i]
if cnt % 2 == 0:
	print(s)
else:
	print('impossible')


a = list(input())
b = list(input())
c = 0
ans = [0] * len(a)
f = 1
for i in range(len(a)):
	if a[i] != b[i]:
		if f:
			ans[i] = a[i]
		else:
			ans[i] = b[i]
		f = 1 - f
		c += 1
	else:
		ans[i] = a[i]
if c % 2 != 0:
	print('impossible')
else:
	print(*ans, sep='')


a = input()
b = input()
s = len(a)
k = True
ans = ''
for i in range(s):
	if a[i] == b[i]:
		ans += a[i]
	else:
		if k:
			ans += a[i]
		else:
			ans += b[i]
		k = not k
if k:
	print(ans)
else:
	print('impossible')


a = input()
b = input()
answer = 0
all_answer = [0] * len(a)
for i in range(len(a)):
	if a[i] != b[i]:
		if answer == 0:
			all_answer[i] = a[i]
			answer += 1
		else:
			all_answer[i] = b[i]
			answer -= 1
	else:
		all_answer[i] = a[i]
if answer == 0:
	print(''.join(all_answer))
else:
	print('impossible')


(a, b, c, cnt) = (input(), input(), '', 0)
for i in range(len(a)):
	if a[i] == b[i]:
		c += a[i]
	else:
		cnt += 1
		if cnt % 2:
			c += a[i]
		else:
			c += b[i]
print('impossible' if cnt & 1 else c)


import sys

def solve():
	(string1, string2) = (input(), input())
	different = []
	T = list(string1)
	turn = 0
	for i in range(len(string1)):
		if string1[i] != string2[i]:
			T[i] = string1[i] if turn == 0 else string2[i]
			turn = (turn + 1) % 2
	if turn:
		print('impossible')
	else:
		print(''.join(T))
solve()


s = input()
t = input()
n = len(s)
which = 0
p = ''
count = 0
for i in range(n):
	if s[i] != t[i]:
		count = count + 1
		if which == 0:
			p = p + s[i]
			which = 1
		else:
			p = p + t[i]
			which = 0
	else:
		p = p + s[i]
if count % 2 == 0:
	print(p)
else:
	print('impossible')


s = input()
t = input()
n = len(s)
num = ''
a = True
for i in range(0, n):
	if s[i] == t[i]:
		num += s[i]
	else:
		if a:
			num += s[i]
		else:
			num += t[i]
		a = not a
if not a:
	print('impossible')
else:
	print(num)


s = input()
d = input()
t = ''
c = True
cnt = 0
for i in range(len(s)):
	if s[i] != d[i]:
		cnt += 1
		if c:
			t += s[i]
			c = False
		else:
			t += d[i]
			c = True
	else:
		t += s[i]
if not t and cnt == 0:
	print(s)
elif t and cnt % 2 == 0:
	print(t)
else:
	print('impossible')


s = input()
t = input()
n = len(s)
f = True
count = 0
ans = ''
for i in range(n):
	if s[i] != t[i]:
		count += 1
		if f:
			ans += s[i]
			f = False
		else:
			ans += t[i]
			f = True
	else:
		ans += s[i]
if count % 2 != 0:
	print('impossible')
else:
	print(ans)


(s, t) = [input() for i in range(2)]
(ans, l, flag) = ('', len(s), 0)
for i in range(l):
	if s[i] != t[i]:
		if flag:
			ans += t[i]
			flag = 0
			continue
		flag = 1
	ans += s[i]
if flag:
	print('impossible')
else:
	print(ans)


import sys
s1 = input()
s2 = input()
a = []
for i in range(len(s1)):
	if s1[i] != s2[i]:
		a.append(i)
if len(a) % 2:
	print('impossible')
	sys.exit()
s = [ch for ch in s1]
for i in a[::2]:
	s[i] = s1[i]
for i in a[1::2]:
	s[i] = s2[i]
for ch in s:
	print(ch, end='')


string1 = list(input())
string2 = list(input())
x = 0
for i in range(len(string1)):
	if string1[i] != string2[i]:
		x += 1
	if x % 2 == 0:
		string1[i] = string2[i]
if x & 1:
	print('impossible')
else:
	print(''.join(string1))


(s, t) = (input(), input())
m = False
ans = ''
for i in range(len(s)):
	x = s[i]
	if s[i] != t[i]:
		m ^= True
		if not m:
			x = t[i]
	ans += x
print('impossible' if m else ans)


s1 = input()
s2 = input()
s3 = []
diff = 0
for i in range(len(s1)):
	if s1[i] == s2[i]:
		s3.append(s1[i])
	else:
		diff += 1
		if diff % 2:
			s3.append(s1[i])
		else:
			s3.append(s2[i])
if diff % 2:
	print('impossible\n')
else:
	print(''.join(s3))


s1 = input()
s2 = input()
diff = 0
n = len(s1)
for i in range(n):
	if s1[i] != s2[i]:
		diff += 1
if diff % 2 == 0:
	ans = ''
	diff2 = 0
	for i in range(n):
		if s1[i] == s2[i]:
			ans += s1[i]
		else:
			if diff2 % 2 == 0:
				ans += s1[i]
			else:
				ans += s2[i]
			diff2 += 1
	print(ans)
else:
	print('impossible')


s = input()
t = input()
final = ''
isS = True
num = 0
for i in range(len(s)):
	if s[i] == t[i]:
		final += s[i]
	else:
		num += 1
		if isS:
			final += s[i]
			isS = False
		else:
			final += t[i]
			isS = True
if num % 2 == 0:
	print(final)
else:
	print('impossible')


a = input()
b = input()
e = 1
k = []
for i in range(len(a)):
	if a[i] == b[i]:
		k.append(a[i])
	elif e == 1:
		k.append(a[i])
		e = 2
	else:
		k.append(b[i])
		e = 1
if e == 2:
	print('impossible')
else:
	for i in range(len(k)):
		print(k[i], end='')


a = input()
b = input()
c = []
num = 0
x = 0
n = len(a)
for i in range(n):
	if a[i] == b[i]:
		c.append(a[i])
	else:
		num += 1
		if x == 0:
			c.append(a[i])
			x = 1
		else:
			c.append(b[i])
			x = 0
if num % 2 == 0:
	str = ''.join(c)
	print(str)
else:
	print('impossible')


s0 = input()
s1 = input()
l = len(s0)
num = 0
res = ''
for c in range(0, l):
	if s0[c] != s1[c]:
		if num % 2 == 0:
			res += s0[c]
		else:
			res += s1[c]
		num += 1
	else:
		res += s0[c]
if num % 2 == 0:
	print(res)
else:
	print('impossible')


a = input()
b = input()
diff = 0
for i in range(len(a)):
	if a[i] != b[i]:
		diff += 1
if diff % 2 != 0:
	print('impossible')
else:
	start = 0
	ans = ''
	for i in range(len(a)):
		if a[i] != b[i]:
			if start % 2 == 0:
				ans += a[i]
			elif start % 2 == 1:
				ans += b[i]
			start += 1
		else:
			ans += a[i]
	print(ans)


s = input()
t = input()
c = 0
for i in range(len(s)):
	if s[i] != t[i]:
		c += 1
if c % 2 != 0:
	print('impossible')
else:
	ch = 0
	out = ''
	for i in range(len(s)):
		if s[i] != t[i]:
			if ch % 2 == 0:
				out += s[i]
				ch += 1
			else:
				out += t[i]
				ch += 1
		else:
			out += s[i]
	print(out)


rdl1 = input()
rdl2 = input()
ans = ''
index1 = 0
index2 = 0
for i in range(len(rdl1)):
	if rdl1[i] == rdl2[i]:
		ans += rdl1[i]
	elif index1 > index2:
		ans += rdl2[i]
		index2 += 1
	else:
		ans += rdl1[i]
		index1 += 1
if index1 == index2:
	print(ans)
else:
	print('impossible')


s = input()
t = input()
arr = [None for i in range(len(s))]
c = 1
g = 0
for i in range(len(s)):
	if s[i] == t[i]:
		arr[i] = s[i]
	else:
		if c % 2 == 1:
			arr[i] = s[i]
		else:
			arr[i] = t[i]
		c += 1
if c % 2 == 0:
	print('impossible')
else:
	print(''.join(map(str, arr)))


s = input()
t = input()
x = ''
l = 0
for i in range(len(s)):
	if s[i] != t[i]:
		if l % 2 == 0:
			x += s[i]
		else:
			x += t[i]
		l += 1
	else:
		x += t[i]
if l % 2 == 1:
	print('impossible')
else:
	print(x)


s1 = input()
s2 = input()
n = len(s1)
ham = 0
for i in range(n):
	if s1[i] != s2[i]:
		ham += 1
if ham & 1:
	print('impossible')
else:
	ham = 0
	for i in range(n):
		if s1[i] == s2[i]:
			print(s1[i], end='')
		else:
			ham += 1
			if ham & 1:
				print(s1[i], end='')
			else:
				print(s2[i], end='')


s1 = input()
s2 = input()
ans = ''
i = 0
j = 0
s1f = True
s2f = False
s1ft = s1f
s2ft = s2f
while i < len(s1) and j < len(s2):
	if s1[i] == s2[j]:
		ans = ans + s1[i]
	else:
		if s1f == True:
			ans = ans + s1[i]
		else:
			ans = ans + s2[j]
		s1f = not s1f
		s2f = not s2f
	i = i + 1
	j = j + 1
if s1ft == s1f and s2ft == s2f:
	print(ans)
else:
	print('impossible')


a = input()
b = input()
n = len(a)
ans = ''
f = True
for i in range(n):
	if a[i] == b[i]:
		ans += a[i]
	else:
		if f:
			ans += a[i]
		else:
			ans += b[i]
		f = not f
if f == True:
	print(ans)
else:
	print('impossible')


s = input().strip()
t = input().strip()
p = []
dif = 0
for (sc, tc) in zip(s, t):
	if sc == tc:
		p.append(sc)
	else:
		dif += 1
		if dif & 1:
			p.append(sc)
		else:
			p.append(tc)
if dif & 1:
	print('impossible')
else:
	print(''.join(p))


a = input()
b = input()
c = ''
first = True
for (a1, b1) in zip(a, b):
	if a1 == b1:
		c += a1
	else:
		if first:
			c += a1
		else:
			c += b1
		first = not first
if first:
	print(c)
else:
	print('impossible')


s = input()
t = input()
n = len(s)
mm = 0
for i in range(n):
	if t[i] != s[i]:
		mm += 1
if mm % 2 == 1:
	print('impossible')
	exit()
c = 0
ans = ''
for i in range(n):
	if t[i] != s[i] and c == 0:
		c = 1
		ans += s[i]
	elif t[i] != s[i] and c == 1:
		c = 0
		ans += t[i]
	else:
		ans += s[i]
print(ans)


a = input()
b = input()
r = []
cont = 0
cont2 = 0
for i in range(len(a)):
	if a[i] != b[i]:
		cont += 1
if cont % 2 == 0:
	for i in range(len(a)):
		if a[i] != b[i]:
			if cont % 2 == 0:
				r.append(a[i])
				cont += 1
			else:
				r.append(b[i])
				cont += 1
		else:
			r.append(a[i])
	for i in range(len(a)):
		print(str(r[i]), end='')
else:
	print('impossible')


s = list(input())
t = list(input())
k = 0
for i in range(len(t)):
	if s[i] != t[i]:
		k += 1
		if k % 2 == 0:
			s[i] = t[i]
if k % 2 == 0:
	print(*s, sep='')
else:
	print('impossible')


s1 = input()
s2 = input()
r = sum((1 for i in range(len(s1)) if s1[i] != s2[i]))
if r % 2 != 0:
	print('impossible')
else:
	one = True
	r = []
	for i in range(len(s1)):
		if s1[i] == s2[i]:
			r.append(s1[i])
		elif one:
			r.append(s1[i])
			one = False
		else:
			r.append(s2[i])
			one = True
	print(''.join(r))


a = input()
b = input()
c = []
res = 0
for (x, y) in zip(a, b):
	if x == y:
		c.append(x)
	else:
		if res == 0:
			c.append(x)
		else:
			c.append(y)
		res ^= 1
if res:
	print('impossible')
else:
	print(''.join(c))


A = input()
B = input()
c = ''
sayac = 0
turn = 0
for i in range(len(A)):
	if A[i] == B[i]:
		c = c + A[i]
	else:
		sayac += 1
		if sayac % 2:
			c = c + A[i]
		else:
			c = c + B[i]
if sayac % 2 == 0:
	print(c)
else:
	print('impossible')