output_description: Print the largest perfect power that is at most X.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      X
attempt: lis=[1,2,4,8,16,32,64,128,256,512,9,27,81,243,729,25,125,625,216,36,343,49,100,1000]
  for i in range(11,32):
      t=i*i
      lis.append(t)
  listt=list(set(lis))
  listt=sorted(listt)
  a=int(input())
  for i in range(300):
      if a < listt[i]:
          print (listt[i-1])
          break
      elif a = listt[i]:
          print(listt[i])
          break
problem_description: Statement
  
  You are given a positive integer X. Find the largest _perfect power_ that is
  at most X. Here, a perfect power is an integer that can be represented as b^p,
  where b is an integer not less than 1 and p is an integer not less than 2.
samples: [{"input": "10", "output": "9\n    \n\nThere are four perfect powers that are at most 10: 1, 4, 8 and 9. We should\nprint the largest among them, 9.\n\n* * *"}, {"input": "1", "output": "1\n    \n\n* * *"}, {"input": "999", "output": "961"}]