output_description: Print the maximum value of D that enables you to visit all the cities.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N X
      x_1 x_2 ... x_N
attempt: N = int(input())
  A = []
  for i in range(N):
     A.append(input())
  S = 0
  for i in range(N-1):
      if A[i][-1] == A[i+1][0]:
          S += 1
  B = 0
  for i in range(N):
      for j in range(N):
          if A[i] == A[j]:
              B += 1
              else:
                  B += 0
  
  if S == N-1 and B == N:
      print('Yes')
  else:
      print('No')
problem_description: Statement
  
  There are N cities on a number line. The i-th city is located at coordinate
  x_i.
  
  Your objective is to visit all these cities at least once.
  
  In order to do so, you will first set a positive integer D.
  
  Then, you will depart from coordinate X and perform Move 1 and Move 2 below,
  as many times as you like:
  
    * Move 1: travel from coordinate y to coordinate y + D.
    * Move 2: travel from coordinate y to coordinate y - D.
  
  Find the maximum value of D that enables you to visit all the cities.
  
  Here, to visit a city is to travel to the coordinate where that city is
  located.
samples: [{"input": "3 3\n    1 7 11", "output": "2\n    \n\nSetting D = 2 enables you to visit all the cities as follows, and this is the\nmaximum value of such D.\n\n  * Perform Move 2 to travel to coordinate 1.\n  * Perform Move 1 to travel to coordinate 3.\n  * Perform Move 1 to travel to coordinate 5.\n  * Perform Move 1 to travel to coordinate 7.\n  * Perform Move 1 to travel to coordinate 9.\n  * Perform Move 1 to travel to coordinate 11.\n\n* * *"}, {"input": "3 81\n    33 105 57", "output": "24\n    \n\n* * *"}, {"input": "1 1\n    1000000000", "output": "999999999"}]