output_description: Print the performance required to achieve the objective.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      R
      G
attempt: c = input()
  t = input()
  lic = list(c)
  lit = list(t)
  ans = []
  lia = []
  n = len(c) - len(t)
  End = False
  for i in range(n + 1):
      hantei = True
      s = "?" * i + t + "?" * (n - i)
      lis = list(s)
      for j in range(len(c)):
          p = lic[j]
          q = lis[j]
          a = p == q
          if a == False and (p != "?" and q != "?"):
              hantei = False
              break
      if hantei == True:
          End = True
          ans = lis
  
      if End == True:
          for i in range(len(c)):
              if lic[i] == "?":
                  lic[i] = ans[i]
          for i in range(len(c)):
              if lic[i] == "?":
                  lic[i] = "a"
  
          lia.append("".join(lic))
  sorted(lia)
  print(lia[0])
  if len(lia) == 0:
      print("UNRESTORABLE")
  
problem_description: Statement
  
  Takahashi is a user of a site that hosts programming contests.  
  When a user competes in a contest, the _rating_ of the user (not necessarily
  an integer) changes according to the _performance_ of the user, as follows:
  
    * Let the current rating of the user be a.
    * Suppose that the performance of the user in the contest is b.
    * Then, the new rating of the user will be the avarage of a and b.
  
  For example, if a user with rating 1 competes in a contest and gives
  performance 1000, his/her new rating will be 500.5, the average of 1 and 1000.
  
  Takahashi's current rating is R, and he wants his rating to be exactly G after
  the next contest.  
  Find the performance required to achieve it.
samples: [{"input": "2002\n    2017", "output": "2032\n    \n\nTakahashi's current rating is 2002.  \nIf his performance in the contest is 2032, his rating will be the average of\n2002 and 2032, which is equal to the desired rating, 2017.\n\n* * *"}, {"input": "4500\n    0", "output": "-4500\n    \n\nAlthough the current and desired ratings are between 0 and 4500, the\nperformance of a user can be below 0."}]