Problem:
 Score: 100 points    Problem Statement We have two distinct integers A and B .  Print the integer K such that |A - K| = |B - K| .  If such an integer does not exist, print IMPOSSIBLE instead.      Constraints  All values in input are integers.  0 \leq A,\ B \leq 10^9  A and B are distinct.         Input Input is given from Standard Input in the following format:  A  B       Output Print the integer K satisfying the condition.  If such an integer does not exist, print IMPOSSIBLE instead.        Sample Input 1 2 16      Sample Output 1 9  |2 - 9| = 7 and |16 - 9| = 7 , so 9 satisfies the condition.       Sample Input 2 0 3      Sample Output 2 IMPOSSIBLE  No integer satisfies the condition.       Sample Input 3 998244353 99824435      Sample Output 3 549034394

Solution (Python):
a,b = map(int,input().split())


ans = (a+b)/2

if ans.is_integer() == True:
  print(int(ans))
else:
  print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
K = (A + B) // 2
if abs(K - A) != abs(K - B):
  print('IMPOSSIBLE')
else:
  print(K)

Solution (Python):
a, b = map(int, input().split())
if abs(a-b) % 2 == 0:
    print((a+b)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
a, b = map(int, input().split())
if (a - b) % 2 == 0:
    print((a + b) // 2)
else:
    print('IMPOSSIBLE')

Solution (Python):
A,B=map(int, input().split())
 
if (A+B)%2==0:
	print(int((A+B)/2))
else:
	print("IMPOSSIBLE")

Solution (Python):
A,B=map(int, input().split())

if (A+B)%2==0:
	print(int((A+B)/2))
else:
	print("IMPOSSIBLE")

Solution (Python):
a,b=map(int,input().split())
if (b-a)/2%1==0:
    s=a+(b-a)//2
else:
    s="IMPOSSIBLE"
print(s)

Solution (Python):
A,B=map(int,input().split())
if (A+B)%2==0:
    print((A+B)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
K = A + B

if K%2 == 0:
  print(K//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
a, b = map(int, input().split())
if (a+b)%2 == 0:
    print(abs(a+b)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
A,B = map(int,input().split())
if(abs(A-B) % 2 == 1):
    print("IMPOSSIBLE")
else:
    print((abs(A-B)//2) + min(A,B))

Solution (Python):


A,B = map(int,input().split())
if (A+B)/2 % 1 == 0:
    print(int((A+B)/2))
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())

if (A + B) & 1 == 1:
    print('IMPOSSIBLE')
else:
    print((A + B) // 2)

Solution (Python):
A,B=map(int,input().split())

if (A-B)%2:
    print("IMPOSSIBLE")
else:
    print((A+B)//2)

Solution (Python):
a, b = map(int, input().split())
if a % 2 == 0 and b % 2 == 1:
    print('IMPOSSIBLE')
elif a % 2 == 1 and b % 2 == 0:
    print('IMPOSSIBLE')
else:
    print((a+b)//2)

Solution (Python):
a,b = map(int,input().split())
if (abs(a+b))%2 == 0:
  print((abs(a+b)//2))
else:
  print('IMPOSSIBLE')

Solution (Python):
def resolve():
    a,b = map(int,input().split())
    if a%2 != b%2:
        print('IMPOSSIBLE')
    else:
        print((a+b)//2)
resolve()

Solution (Python):
A,B=map(int,input().split())
if A>B:
  if (A-B)%2==0:
    print(B+(A-B)//2)
  else:
    print("IMPOSSIBLE")
else:
  if (B-A)%2==0:
    print(A+(B-A)//2)
  else:
    print("IMPOSSIBLE")

Solution (Python):
a,b=map(int, input().split())
print((a+b)//2 if (a+b)%2==0 else 'IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())

if a == - b :
    print('IMPOSSIBLE')
elif (a+b)//2 != (a+b)/2:
    print('IMPOSSIBLE')
else:
    print((a+b)//2)

Solution (Python):
A,B = map(int,input().split())

if (A + B) % 2 == 0:
    print((A+B) // 2)
else:
    print("IMPOSSIBLE")

Solution (Python):
A,B = map(int,input().split())
if abs(A-B) % 2 == 0:
    print(min(A,B) + abs(A-B)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
a,b = map(int,input().split())

if (a + b) % 2 == 0 :
  print((a+b)//2)
else:
  print('IMPOSSIBLE')

Solution (Python):
a,b = map(int,input().split())
if (a+b)%2==0:
    print((a+b)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
a,b=map(int,input().split())
print((a+b)//2 if (a+b)%2==0 else 'IMPOSSIBLE')

Solution (Python):
a,b = map(int,input().split())
print("IMPOSSIBLE" if a%2 != b%2 else (a+b)//2)

Solution (Python):
A, B = map(int, input().split())

if (A+B)%2 != 0:
    print("IMPOSSIBLE")
else:
    K = int((A+B)/2)
    print(K)

Solution (Python):
a, b = map(int,input().split())
if (a + b) % 2 == 0:
    print((a + b) // 2)
else:
    print('IMPOSSIBLE')

Solution (Python):
A, B = map(int, input().split())

K = (A+B) // 2
if (A+B)%2 == 0:
  print(K)
else:
  print("IMPOSSIBLE")

Solution (Python):
a,b = map(int,input().split())
if (a - b) % 2 == 0:
    print(int((a+b)/2))
else:
    print('IMPOSSIBLE')

Solution (Python):
a = list(map(int,input().split()))
A = a[0]
B = a[1]

if (A+B) % 2 == 0:
    print((A+B)//2)
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b=map(int,input().split())
x=(a+b)/2
if x.is_integer():
    print(int(x))
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
print ("IMPOSSIBLE" if (A+B) % 2 > 0 else (A+B)//2)

Solution (Python):
a, b = map(int, input().split())
print((a + b) // 2 if (a + b) % 2 == 0 else 'IMPOSSIBLE')

Solution (Python):
A, B = map(int, input().split())
if (A + B) % 2 != 0:
  print("IMPOSSIBLE")
else:
  print(int((A+B)/2))

Solution (Python):
A,B=map(int,input().split())
if abs(A-B)%2==0:
    print((A+B)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
K = (A + B) // 2
if abs(A - K) == abs(K - B):
    print(K)
else:
    print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split(' '))
if (a - b) % 2 == 1:
    print('IMPOSSIBLE')
else:
    print((a + b) // 2)

Solution (Python):
a, b = map(int,input().split())
if (a > b):
  a, b = b, a
if ((b - a)%2 == 0):
  print(a + (b - a)//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
K = (A + B) // 2
if abs(A - K) == abs(K - B):
    print(K)
else:
    print('IMPOSSIBLE')

Solution (Python):
A, B = map(int, input().split())
 
if (A+B) %2 == 0: print((A+B) // 2)
else: print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())

if abs(a + b) % 2 == 0:
    print(abs(a + b) // 2)
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b=map(int, input().split())
if ((a+b)/2).is_integer():
    print((a+b)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
a, b = map(int, input().split())
if (a+b) % 2 == 0:
    print((a+b)//2)
else:
    print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())
if (a + b) % 2 == 0: print((a + b) // 2)
else: print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())
print((a+b)//2 if (a+b)%2 == 0 else 'IMPOSSIBLE')

Solution (Python):
"""
    こんにちは。これはクシャルです
    
    Author : thekushalghosh (クシャル)
    Team   : CodeDiggers
 
    I prefer Python language over the C++ language :p :D
        
    Visit my website : thekushalghosh.github.io
"""
import sys,math,cmath,time
start_time = time.time()


    
def solve():
    a,b = invr()
    if abs(a - b) % 2 == 0:
        print((a + b) // 2)
    else:
        print("IMPOSSIBLE")
    


 
def main():
    global tt
    if not ONLINE_JUDGE:
        sys.stdin = open("input.txt","r")
        sys.stdout = open("output.txt","w")
    t = 1
    for tt in range(t):
        solve()
    if not ONLINE_JUDGE:
        print("Time Elapsed :",time.time() - start_time,"seconds")
        sys.stdout.close()
    

def inp():
    return(int(input()))
def inlt():
    return(list(map(int,input().split())))
def insr():
    return(input().strip())
def invr():
    return(map(int,input().split()))
 

def counter(a):
    q = [0] * max(a)
    for i in range(len(a)):
        q[a[i] - 1] = q[a[i] - 1] + 1
    return(q)

def counter_elements(a):
    q = dict()
    for i in range(len(a)):
        if a[i] not in q:
            q[a[i]] = 0
        q[a[i]] = q[a[i]] + 1
    return(q)

def string_counter(a):
    q = [0] * 26
    for i in range(len(a)):
        q[ord(a[i]) - 97] = q[ord(a[i]) - 97],1
    return(q)
 
def factors(n):
    q = []
    for i in range(1,int(n ** 0.5) + 1):
        if n % i == 0: q.append(i); q.append(n // i)
    return(list(sorted(list(set(q)))))
 
def prime_factors(n):
    q = []
    while n % 2 == 0: q.append(2); n = n // 2
    for i in range(3,int(n ** 0.5) + 1,2):
        while n % i == 0: q.append(i); n = n // i
    if n > 2: q.append(n)
    return(list(sorted(q)))

def transpose(a):
    n,m = len(a),len(a[0])
    b = [[0] * n for i in range(m)]
    for i in range(m): 
        for j in range(n): 
            b[i][j] = a[j][i]
    return(b)


ONLINE_JUDGE = __debug__
if ONLINE_JUDGE:
    input = sys.stdin.readline
main()

Solution (Python):
A, B = map(int, input().split())
if (A + B) % 2 == 0:
    print((A + B) // 2)
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
if A > B:
  A, B = B, A
if abs(A - B) % 2 != 0:
  print("IMPOSSIBLE")
  exit()
print(A + (abs(A-B) // 2))

Solution (Python):
a, b = map(int, input().split())
print((a + b) // 2 if (a + b) % 2  == 0 else 'IMPOSSIBLE')

Solution (Python):
a,b=map(int,input().split())
if (a+b)%2==0:
  print((a+b)//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
a,b = map(int,input().split())
k = (a + b)//2
if a + b == 2 * k:
    print(k)
else:
    print('IMPOSSIBLE')

Solution (Python):
A,B=map(int,input().split())
print((A+B)//2 if (A+B)%2==0 else "IMPOSSIBLE")

Solution (Python):
a, b = map(int, input().split())
if (a + b) % 2 == 0:
    print(int((a + b) / 2))
else:
    print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())
ans = (a**2-b**2)/(2*(a-b))

if ans.is_integer():
    print(int(ans))
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b=map(int,input().split())

if (a+b)%2==0:
    print(int((a+b)/2))
else :
    print('IMPOSSIBLE')

Solution (Python):
A,B = map(int,input().split())
answer = 'IMPOSSIBLE'
if (A+B)%2==0:
    answer = (A+B)//2
    
print(answer)

Solution (Python):
a= list(map(int,input().split()))
if (a[0]+a[1]) % 2 == 0:
  print((a[0]+a[1])//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())

if (A + B) % 2 == 0:
    print(int((A + B) / 2))
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b=map(int,input().split())
if (a+b)%2==0:
    print(int((a+b)/2))
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
print((A + B) // 2 if (A + B) % 2 == 0 else "IMPOSSIBLE")

Solution (Python):
a, b = map(int, input().split( ))
s = a + b
if s %2 ==1:
  print('IMPOSSIBLE')
else:
  print(s//2)

Solution (Python):
A,B=map(int,input().split())
print((A+B)//2) if (A+B)%2==0 else print('IMPOSSIBLE')

Solution (Python):
A,B=map(int,input().split(' '))
if (A+B)%2!=0:
    print("IMPOSSIBLE")
else:
    print((A+B)//2)

Solution (Python):
a,b=map(int,input().split())
if (a+b)%2==0:
  print((a+b)//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
a,b=map(int,input().split())
if (a+b)%2 == 0 :
  print(int((a+b)/2))
else :
  print('IMPOSSIBLE')

Solution (Python):
import bisect, collections, copy, heapq, itertools, math, string, sys
input = lambda: sys.stdin.readline().rstrip() 
sys.setrecursionlimit(10**7)
INF = float('inf')
def I(): return int(input())
def F(): return float(input())
def SS(): return input()
def LI(): return [int(x) for x in input().split()]
def LI_(): return [int(x)-1 for x in input().split()]
def LF(): return [float(x) for x in input().split()]
def LSS(): return input().split()

def resolve():
    A, B = LI()

    if (A - B) % 2 == 0:
        print((A + B) // 2)
    else:
        print('IMPOSSIBLE')

if __name__ == '__main__':
    resolve()

Solution (Python):
a, b = map(int, input().split())
k = (a * a - b * b) / (2 * a - 2 * b)
if k == int(k):
    print(int(k))
else:
    print('IMPOSSIBLE')

Solution (Python):
import sys

readline = sys.stdin.readline
MOD = 10 ** 9 + 7
INF = float('INF')
sys.setrecursionlimit(10 ** 5)


def main():
    A, B = map(int, readline().split())
    A, B = min(A, B), max(A, B)

    if (B - A) % 2 == 1:
        print("IMPOSSIBLE")
    else:
        print((A + B) // 2)


if __name__ == '__main__':
    main()

Solution (Python):
a,b=map(int, input().split())

if (a+b)%2==0:
    print((a+b)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
a,b = [int(v) for v in input().split()]
if abs(a-b) % 2 == 0:
    print(int((max(a,b)+min(a,b))/2))
else:
    print("IMPOSSIBLE")

Solution (Python):
a, b = map(int, input().split())
if (a + b) % 2 == 0:
    print((a + b) // 2)
else:
    print('IMPOSSIBLE')

Solution (Python):
a=sorted(list(map(int,input().split())))
if a[1]%2==a[0]%2:
  print(a[0]+(a[1]-a[0])//2)
else:
  print('IMPOSSIBLE')

Solution (Python):
A,B=map(int,input().split())
x=(A**2-B**2)/(2*(A-B))
if x%1==0:
    print(int(x))
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b = map(int,input().split())
if (a-b) % 2 == 0:
  print((a+b)//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
import sys
import itertools
tokens = itertools.chain.from_iterable(map(str.split, sys.stdin))

no = 'IMPOSSIBLE'
a = int(next(tokens))
b = int(next(tokens))


k = (a**2 - b**2) // (2 * (a - b))
if abs(a - k) != abs(b - k):
    print(no)
else:
    print(k)

Solution (Python):
def LI():
    return list(map(int, input().split()))


A, B = LI()
if (A+B) % 2 == 0:
    ans = (A+B)//2
else:
    ans = "IMPOSSIBLE"
print(ans)

Solution (Python):
a,b=map(int,input().split())
if abs(a-b)%2==0:
  print((a+b)//2)
else:
  print('IMPOSSIBLE')

Solution (Python):
A,B=map(int,input().split())

if (A+B)%2==1:
    print("IMPOSSIBLE")
else:
    print((A+B)//2)

Solution (Python):
a,b=map(int,input().split())
if abs(a-b)%2==0:
    k=max(a,b)-abs(a-b)//2
    print(k)
    
else:
    print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())
print('IMPOSSIBLE' if (a ^ b) & 1 else (a + b) >> 1)

Solution (Python):



from fractions import gcd
from itertools import combinations,permutations,accumulate, product 

from collections import deque,defaultdict,Counter
import decimal
import re
import math















import sys
sys.setrecursionlimit(10000000)
mod = 10**9 + 7


from sys import stdin
readline = stdin.readline
def readInts():
  return list(map(int,readline().split()))
def readTuples():
    return tuple(map(int,readline().split()))
def I():
  return int(readline())
a,b = readInts()
print((a+b)//2 if (a+b)%2 == 0 else 'IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())


if a == b:
    print(0)
elif (a + b) % 2 == 0:
    print((a + b) // 2)
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
if abs(A-B)%2 == 0:
  print(min(A,B) + abs(A-B)//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
a,b = map(int,input().split())
print((a+b)//2 if (a+b)%2==0 else "IMPOSSIBLE")

Solution (Python):
A,B = map(int,input().split())
if A>B:
    A,B = B,A
if (B-A)%2==0:
    print((B+A)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
a, b = map(int, input().split())
if (a + b) % 2 == 0:
    print((a + b) // 2)
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
if A > B: A, B = B, A
if (B - A) & 1:
    print('IMPOSSIBLE')
    exit()
print(A + (B - A) // 2)

Solution (Python):
A, B = map(int, input().split())
if A > B:
    A, B = B, A
diff = B - A
if diff % 2:
    print("IMPOSSIBLE")
else:
    print(A + diff // 2)

Solution (Python):
a,b = map(int, input().split())
if (a-b)%2 == 1:
    print('IMPOSSIBLE')
else:
    ans = abs(a-b)//2 + min(a,b)
    print(ans)

Solution (Python):
A, B = map(int, input().split())

if (A+B)%2 == 0:
    print(int((A+B)/2))
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
K = A+B
if K%2:
    print('IMPOSSIBLE')
else:
    print(K//2)

Solution (Python):
a,b=map(int,input().split())
if (a-b)%2==0:
  print((a+b)//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
a,b= map(int,input().split())
if (b+a)%2==0:
  print((a+b)//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
a, b = map(int,input().split())
if (a + b) % 2 == 0:
  print((a + b)//2)
else:
  print('IMPOSSIBLE')

Solution (Python):
a,b = map(int,input().split())
print((a+b)//2 if (a+b)%2==0 else "IMPOSSIBLE")

Solution (Python):
A,B=map(int,input().split())
K=(A**2-B**2)/(2*(A-B))
if K%1==0:
  print(int(K))
else:
  print('IMPOSSIBLE')

Solution (Python):
A, B = map(int,input().split())
if (A+B) % 2 == 0:
    print(int((A+B)/2))
else:
    print('IMPOSSIBLE')

Solution (Python):
def main():
    A, B = map(int, input().split())

    if (A + B) % 2 == 0:
        ans = (A + B) // 2
    else:
        ans = "IMPOSSIBLE"

    print(ans)


if __name__ == "__main__":
    main()

Solution (Python):
def mapt(fn, *args):
    return tuple(map(fn, *args))


def Input():
    return mapt(int, input().split(" "))


def main():
    a, b = Input()
    if a % 2 !=  b % 2:
        print("IMPOSSIBLE")
    else:
        print((a+b)//2)

main()

Solution (Python):
a, b = map(int, input().split())
x = abs(a - b)
if x % 2:
    print('IMPOSSIBLE')
else:
    print(int(abs(a+b)/2))

Solution (Python):
A, B = map(int, input().split())
if (A - B) % 2 == 1:
  print("IMPOSSIBLE")
else:
  print((A+B)//2)

Solution (Python):
a,b=map(int,input().split())
c=abs(a+b)
if c%2==0:
  print(c//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
a,b=[int(x) for x in input().split()]
k=(a+b)//2
if (a+b)%2==0:
  print(k)
else:
  print("IMPOSSIBLE")

Solution (Python):
n, k = map(int, input().split())
summ = n + k
if summ % 2 != 0:
    print('IMPOSSIBLE')
else:
    print(summ//2)

Solution (Python):
a, b = [int(n) for n in input().split()]

if (a+b) % 2 == 0:
    print(int((a+b)/2))
else:
    print("IMPOSSIBLE")

Solution (Python):
a, b = map(int, input().split())

if (max(a,b)-min(a,b))%2 == 0:
    print((max(a,b)-min(a,b))//2+min(a,b))
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b=input().split()
a=int(a)
b=int(b)
if (a+b)%2==0:
  print(int((a+b)/2))
else:
  print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
print(int((A+B)/2) if (A+B)%2==0 else 'IMPOSSIBLE')

Solution (Python):
a,b=map(int,input().split())
if((a+b)%2)==0:
    print((a+b)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
A,B = map (int, input ().split ())
X = (A+B)/2
if X%1 == 0:
  print (round(X))
else:
  print ('IMPOSSIBLE')

Solution (Python):
A, B = map(int, input().split())

if (A+B) % 2 == 0:
    print((A+B)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())

if A == B:
    print(0)

elif (A+B)%2 == 0:
    print((A+B)//2)

else:
    print("IMPOSSIBLE")

Solution (Python):
x,y=map(int,input().split())
s=x+y
if(s%2==0):
    print(s//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
a,b = input().split()
a =int(a)
b = int(b)

if (a + b) % 2 ==0:
  print((a+b)//2)
else:
  print('IMPOSSIBLE')

Solution (Python):
a,b=map(int,input().split())
if (a+b)%2 is not 0:
   print('IMPOSSIBLE')
else:
   print((a+b)//2)

Solution (Python):
A,B = map(int,input().split())

if ((A+B)/2)%1 == 0:
    print(abs((A+B))//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
A,B = map(int,input().split())

if (A+B)%2 == 0:
  print((A+B)//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
if (A + B) % 2 == 0:
    print((A + B) // 2)
else:
    print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())
print((a + b) // 2 if (a + b) % 2 == 0 else "IMPOSSIBLE")

Solution (Python):
a, b = map(int, input().split())
if (a-b) % 2 == 0:
    print((a+b)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
if (A + B) % 2 == 0:
    print(int((A + B) / 2))
else:
    print('IMPOSSIBLE')

Solution (Python):

def main():
    A, B = map(int, input().split())

    print('IMPOSSIBLE') if (A + B) % 2 else print((A + B) // 2)


if __name__ == '__main__':
    main()

Solution (Python):
a,b = map(int,input().split(" "))
if a%2 != b%2:
  print('IMPOSSIBLE')
else:
  print((a+b)//2)

Solution (Python):
a, b = map(int,input().split())
if (a+b)%2 == 1:
    print('IMPOSSIBLE')
else:
    print((a+b)//2)

Solution (Python):
a,b = map(int,input().split())

if (a+b)%2==0:
    print((a+b)//2)
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b=map(int,input().split())

if (a+b)%2==0:
    print((a+b)//2)
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b = map(int, input().split())
ab = (a+b)/2
if ab.is_integer() == True:
    print(int(ab))
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b = map(int,input().split(" "))
if a%2 != b%2:
  print('IMPOSSIBLE')
else:
  print((a+b)//2)

Solution (Python):




a, b = map(int, input().strip().split())
diff = abs(a-b)
if diff % 2 == 0:
    print(int((a+b)/2))
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b = map(int,input().split())

if (a+b) % 2 == 0:
    print((a+b)//2)
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b = map(int,input().split())
if (a+b)%2 == 0:
    print(int((a+b)/2))
else:
    print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
if (A + B) % 2 == 0:
    print(int((A + B) / 2))
else:
    print("IMPOSSIBLE")

Solution (Python):
a, b = map(int,input().split())

if (a+b)%2 != 0:
    print('IMPOSSIBLE')
else:
    print(int((a+b)//2))

Solution (Python):
a, b = sorted(map(int, input().split()))
if a - b == 2 * int((a - b) / 2):
    print(int((a + b) / 2))
else:
    print("IMPOSSIBLE")

Solution (Python):
ma = lambda :map(int,input().split())
lma = lambda :list(map(int,input().split()))
tma = lambda :tuple(map(int,input().split()))
ni = lambda:int(input())
yn = lambda fl:print("Yes") if fl else print("No")
import collections
import math
import itertools
import heapq as hq
a,b = ma()
k2 = abs(b-a)
if k2%2==0:
    print(k2//2+min(b,a))
else:
    print("IMPOSSIBLE")

Solution (Python):
a, b = map(int, input().split())
if (a+b)%2 != 0: 
	print("IMPOSSIBLE")
else: 
	print((a + b) // 2)

Solution (Python):
a,b=map(int,input().split())

if (a+b)%2!=0:
  print("IMPOSSIBLE")
  
else:
  print((a+b)//2)

Solution (Python):
nums = list(map(int,input().split()))
A = nums[0]
B = nums[1]
if abs(A-B) % 2 != 0:
  print("IMPOSSIBLE")
else:
  mini = min(A,B)
  print((A+B)//2)

Solution (Python):
a,b = map(int, input().split())
if (a+b)%2 == 0:
  print((a+b)//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
A, B = list(map(int, input().split()))
if (A + B) % 2 != 0:
	print('IMPOSSIBLE')
else:
	K = (A + B) // 2
	print(K)

Solution (Python):

def main():
    a, b = map(int, input().split())
    if (a + b) % 2 == 0:
        print(int((a + b) / 2))
    else:
        print('IMPOSSIBLE')


if __name__ == "__main__":
    main()

Solution (Python):
a, b = map(int, input().split())
if (a + b) % 2 == 0: print((a + b) // 2)
else: print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())
print((A + B) // 2) if A % 2 == B % 2 else print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())

if A % 2 == B % 2:
    print((A + B) // 2)
else:
    print("IMPOSSIBLE")

Solution (Python):
m, n = map(int, input().split())
total = m + n
if total % 2 == 0:
  print(total // 2)
else:
  print('IMPOSSIBLE')

Solution (Python):
A, B = map(int,input().split())

if (A+B) % 2 == 0:
    print((A+B)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
a, b = map(int, input().split())
x = max(a, b)
y = min(a, b)
if (x - y) % 2:
  print("IMPOSSIBLE")
else:
  print(y + int((x - y) / 2))

Solution (Python):
a,b=map(int,input().split())
ans="IMPOSSIBLE"
if a%2==b%2:
    ans=int((a+b)/2)
print(ans)

Solution (Python):
a, b = list(map(int, input().split()))

if (a + b) % 2 == 1:
    print("IMPOSSIBLE")
else:
    print((a + b) // 2)

Solution (Python):
A,B=map(int,input().split())
print(min(A,B)+abs(A-B)//2 if abs(A-B)//2*2==abs(A-B) else 'IMPOSSIBLE')

Solution (Python):
A, B = map(int, input().split())
if (A + B) % 2:
    print('IMPOSSIBLE')
else:
    print((A + B) // 2)

Solution (Python):
a,b=map(int,input().split())

ans=(a+b)//2

if ans==(a+b)/2:
    print(ans)
else:
    print('IMPOSSIBLE')

Solution (Python):
A, B = map(int, input().split())
ans = int((A+B)/2) if (A+B) % 2 == 0 else "IMPOSSIBLE"
print(ans)

Solution (Python):
def main():
    a, b = map(int, input().split())
    k = (a+b) / 2

    if k==int(k):
        print(int(k))
    else:
        print('IMPOSSIBLE')

if __name__ == '__main__':
    main()

Solution (Python):
a, b = map(int, input().split())
if (a + b) % 2 == 0:
    print((a + b) // 2)
else:
    print('IMPOSSIBLE')

Solution (Python):
A, B = map(int, input().split())
if A < B:
    A, B = B, A
if A==B:
    print(0)
elif (A+B)%2 == 0:
    print((A+B)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
N,M=map(int,input().split())
if (N+M)%2==0:
  print((N+M)//2)
else:
  print("IMPOSSIBLE")

Solution (Python):
a, b = list(map(int, input().split()))
print((a + b) // 2 if a % 2 == b % 2 else "IMPOSSIBLE")

Solution (Python):
A,B = map(int,input().split())
print("IMPOSSIBLE" if (A+B)%2!=0 else int((A+B)/2))

Solution (Python):
a,b=map(int,input().split())
print((a+b)//2 if (a+b)%2==0 else "IMPOSSIBLE")

Solution (Python):
import math

A, B = map(int, input().split())

if A % 2 == B % 2:
    K = abs(B - A) / 2
    if A > B:
        print(A - math.ceil(K))
    else:
        print(B - math.ceil(K))
else:
    print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())
if abs(a - b) % 2 == 0:
    print(max(a, b) - abs(a - b) // 2)
else:
    print('IMPOSSIBLE')

Solution (Python):
a,b = map(int,input().split())
if a%2 != b%2:
    print('IMPOSSIBLE')
else:
    print(abs((a+b)//2))

Solution (Python):
a, b = map(int, input().split())

if (a+b) % 2 == 0:
  print((a+b)//2)
else:
  print('IMPOSSIBLE')

Solution (Python):
a,b = map(int,input().split())
if a % 2 == 0 and b % 2 == 1:
    print('IMPOSSIBLE')
elif a % 2 == 1 and b % 2 == 0:
    print('IMPOSSIBLE')
else:
    print((a+b) // 2)

Solution (Python):
a, b = map(int, input().split())

if (a + b) % 2 == 0:
  print((a + b) // 2)
  
else:
  print('IMPOSSIBLE')

Solution (Python):
a, b = list(map(int, input().split()))
n = a + b
if n % 2 == 0:
  print(int(n/2))
else:
  print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())
if (a + b) % 2 != 0:
  print("IMPOSSIBLE")
else:
  print((a + b) // 2)

Solution (Python):
a,b = map(int, input().split())

k = (a**2-b**2)/(2*(a-b))

if k.is_integer() == False:
    print("IMPOSSIBLE")
else:
    print(int(k))

Solution (Python):
a,b = map(int,input().split())

if abs(b-a)%2!=0:
    print("IMPOSSIBLE")
else:
    print((a+b)//2)

Solution (Python):
A, B = map(int, input().split(' '))
if (A + B) % 2 == 0:
    print(int((A + B) / 2))
else:
    print('IMPOSSIBLE')

Solution (Python):





a, b = map(int, input().split())

if (a+b)%2 != 0:
    print("IMPOSSIBLE")
else:
    print((a+b)//2)

Solution (Python):
import sys
def input(): return sys.stdin.readline().strip()
def mapint(): return map(int, input().split())
sys.setrecursionlimit(10**9)

A, B = mapint()
if abs(A-B)%2==1:
    print('IMPOSSIBLE')
else:
    print((A+B)//2)

Solution (Python):
a,b=list(map(int,input().split()))
if (a+b)%2==0:
  print(int((a+b)/2))
else:
  print('IMPOSSIBLE')

Solution (Python):
import sys
sys.setrecursionlimit(10**7) 
import math
from copy import copy, deepcopy
from copy import deepcopy as dcp
from operator import itemgetter
from bisect import bisect_left, bisect, bisect_right

from collections import deque, defaultdict


from collections import Counter

from itertools import accumulate,combinations,permutations,product

from heapq import heapify,heappop,heappush

from functools import reduce,lru_cache

from decimal import Decimal

def input(): 
    x=sys.stdin.readline()
    return x[:-1] if x[-1]=="\n" else x
def printe(*x):print("
def printl(li): _=print(*li, sep="\n") if li else None
def argsort(s, return_sorted=False): 
    inds=sorted(range(len(s)), key=lambda k: s[k])
    if return_sorted: return inds, [s[i] for i in inds]
    return inds
def alp2num(c,cap=False): return ord(c)-97 if not cap else ord(c)-65
def num2alp(i,cap=False): return chr(i+97) if not cap else chr(i+65)
def matmat(A,B):
    K,N,M=len(B),len(A),len(B[0])
    return [[sum([(A[i][k]*B[k][j]) for k in range(K)]) for j in range(M)] for i in range(N)]
def matvec(M,v):
    N,size=len(v),len(M)
    return [sum([M[i][j]*v[j] for j in range(N)]) for i in range(size)]
def T(M):
    n,m=len(M),len(M[0])
    return [[M[j][i] for j in range(n)] for i in range(m)]
def binr(x): return bin(x)[2:]
def bitcount(x): 
    x= x - ((x >> 1) & 0x5555555555555555)
    x= (x & 0x3333333333333333) + ((x >> 2) & 0x3333333333333333)
    x= (x + (x >> 4)) & 0x0f0f0f0f0f0f0f0f 
    x+= (x >> 8); x+= (x >> 16); x+= (x >> 32) 
    return x & 0x7f

def main():
    mod = 1000000007
    

    
    A,B = map(int, input().split())
    
    
    
    if (A+B)%2==1:
        print('IMPOSSIBLE')
    else:
        print((A+B)//2)





if __name__ == "__main__":
    main()

Solution (Python):
a, b = map(int, input().split())
if (a+b)%2==0:
	print((a+b)//2)
else:
	print('IMPOSSIBLE')

Solution (Python):
a,b=list(map(int,input().split()))
if a==b:
  print(0)
else:
  if (a+b)%2==0:
    print((a+b)//2)
  else:
    print("IMPOSSIBLE")

Solution (Python):
a,b = map(int,input().split())
print((a+b)//2 if (a+b)%2==0 else 'IMPOSSIBLE')

Solution (Python):
A=sorted(list(map(int,input().split())))
a=A[0]
b=A[1]
if (b-a)%2==0:
    print(a+(b-a)//2)
else:
    print("IMPOSSIBLE")

Solution (Python):
a, b = [int(i) for i in input().split(" ")]
print("IMPOSSIBLE" if (a+b)%2 else (a+b)//2)

Solution (Python):
a, b = map(int, input().split())
print((a + b) // 2) if ((a + b) / 2) % 1 == 0 else print('IMPOSSIBLE')

Solution (Python):
tmp = input().split(" ")

A = int(tmp[0])
B = int(tmp[1])

print(int((A+B)/2)) if (A + B) % 2 == 0 else print("IMPOSSIBLE")

Solution (Python):
A, B = map(int, input().split())

if A == B:
    print(1)
elif (A + B) % 2 == 0:
    K = (A + B) // 2
    if abs(A - K) == abs(B - K):
        print(K)
else:
    print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())
ans = abs(a - b) / 2
if ans.is_integer():
    ans = max(a, b) - int(ans)
    print(ans)
else:
    print("IMPOSSIBLE")

Solution (Python):


a, b = map(int, input().split())

print((a+b)//2 if (a+b)%2==0 else 'IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())

if (a + b) % 2 == 0:
    print((a + b) // 2)
else:
    print("IMPOSSIBLE")

Solution (Python):


def main():

    A, B = map(int, input().split())

    if (A + B) % 2 == 0:
        ans = (A + B) // 2

    else:
        ans = 'IMPOSSIBLE'

    print(ans)


if __name__ == "__main__":
    main()

Solution (Python):
a,b=map(int,input().split())
if (a+b)%2==1:
    print('IMPOSSIBLE')
else:
    print((a+b)//2)

Solution (Python):
a, b = map(int, input().split())
k = (a ** 2 - b **2) / 2 / (a - b)

if k.is_integer():
  print(int(k))
else:
  print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())
A = (a+b)/2
print(int(A) if (a+b)%2==0 else "IMPOSSIBLE")

Solution (Python):
a,b=map(int,input().split());print(['IMPOSSIBLE',a+(b-a)//2][(b-a)%2==0])

Solution (Python):
a,b=map(int, input().split())
if (a+b)%2==0:
  print((a+b)//2)
else:
  print('IMPOSSIBLE')

Solution (Python):
a, b = map(int, input().split())

if (a + b) % 2 == 0:
    print((a + b) // 2)
else:
    print("IMPOSSIBLE")