output_description: Print the value \sum_{K=1}^N K\times f(K).
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
attempt: def yakusu(x):
      save = []
      for i in range(1, x + 1):
          if x % i == 0:
              save.append(i)
      return len(save)
  
  
  n = input()
  
  sum_yakusu = 0
  
  for i in range(1, n + 1):
      tmp = i * yakusu(i)
      sum_yakusu += tmp
  
  print(sum_yakusu)
  
problem_description: Statement
  
  For a positive integer X, let f(X) be the number of positive divisors of X.
  
  Given a positive integer N, find \sum_{K=1}^N K\times f(K).
samples: [{"input": "4", "output": "23\n    \n\nWe have f(1)=1, f(2)=2, f(3)=2, and f(4)=3, so the answer is 1\\times 1 +\n2\\times 2 + 3\\times 2 + 4\\times 3 =23.\n\n* * *"}, {"input": "100", "output": "26879\n    \n\n* * *"}, {"input": "10000000", "output": "838627288460105\n    \n\nWatch out for overflows."}]