output_description: Print the maximum possible value of M_1 + M_2 + \cdots + M_N.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
attempt: print(int((lambda n: n * (n + 1) / 2 - n)(int(input()))))
  
problem_description: Statement
  
  For an integer N, we will choose a permutation \\{P_1, P_2, ..., P_N\\} of
  \\{1, 2, ..., N\\}.
  
  Then, for each i=1,2,...,N, let M_i be the remainder when i is divided by P_i.
  
  Find the maximum possible value of M_1 + M_2 + \cdots + M_N.
samples: [{"input": "2", "output": "1\n    \n\nWhen the permutation \\\\{P_1, P_2\\\\} = \\\\{2, 1\\\\} is chosen, M_1 + M_2 = 1 + 0\n= 1.\n\n* * *"}, {"input": "13", "output": "78\n    \n\n* * *"}, {"input": "1", "output": "0"}]