output_description: Find the minimum number of moves required to achieve the objective.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N M
      X_1 X_2 ... X_M
attempt: from sys import stdin
  
  
  ############################################
  # from sys import stdin
  import numpy as np
  
  # read data for n sequences.
  input = stdin.readline().split()
  m = int(input[0])
  n = int(input[1])
  # n = int(stdin.readline().split()[1])
  data = np.zeros(n)
  d = stdin.readline().split()
  for i, x in enumerate(d):
      data[i] = int(x)
  data = sorted(data)
  
  dif = np.zeros(len(data) - 1)
  for x in range(0, len(data) - 1):
      dif[x] = data[x + 1] - data[x]
  
  out = 0
  
  # split in m data.
  # print(data)
  dif = np.zeros(len(data) - 1)
  for x in range(0, len(data) - 1):
      dif[x] = data[x + 1] - data[x]
  out = sum(sorted(dif, reverse=True)[m - 1 :])
  
  
  print(int(out))
  
problem_description: Statement
  
  We will play a one-player game using a number line and N pieces.
  
  First, we place each of these pieces at some integer coordinate.
  
  Here, multiple pieces can be placed at the same coordinate.
  
  Our objective is to visit all of the M coordinates X_1, X_2, ..., X_M with
  these pieces, by repeating the following move:
  
  **Move** : Choose a piece and let x be its coordinate. Put that piece at
  coordinate x+1 or x-1.
  
  Note that the coordinates where we initially place the pieces are already
  regarded as visited.
  
  Find the minimum number of moves required to achieve the objective.
samples: [{"input": "2 5\n    10 12 1 2 14", "output": "5\n    \n\nThe objective can be achieved in five moves as follows, and this is the\nminimum number of moves required.\n\n  * Initially, put the two pieces at coordinates 1 and 10.\n  * Move the piece at coordinate 1 to 2.\n  * Move the piece at coordinate 10 to 11.\n  * Move the piece at coordinate 11 to 12.\n  * Move the piece at coordinate 12 to 13.\n  * Move the piece at coordinate 13 to 14.\n\n* * *"}, {"input": "3 7\n    -10 -3 0 9 -100 2 17", "output": "19\n    \n\n* * *"}, {"input": "100 1\n    -100000", "output": "0"}]