output_description: If it is estimated that Hikuhashi will never become Kaiden, print `-1`.
  Otherwise, print the estimated number of contests before he become Kaiden for
  the first time.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      K A B
attempt: s =input().split()
  a=0
  b=0
  while a<int(s[0]) :
      b+=1
      a+=int(s[1])
      if a>int(s[0]) :
          break
      b+=1
      a=a-int(s[2])
      if a<0 :
          break
  if a<0 :
      print(-1)
  if a>int(s[0]) :
      print(int(b)
problem_description: Statement
  
   _ButCoder Inc._ runs a programming competition site called _ButCoder_. In
  this site, a user is given an integer value called rating that represents
  his/her skill, which changes each time he/she participates in a contest. The
  initial value of a new user's rating is 0, and a user whose rating reaches K
  or higher is called _Kaiden_ ("total transmission"). Note that a user's rating
  may become negative.
  
  Hikuhashi is a new user in ButCoder. It is estimated that, his rating
  increases by A in each of his odd-numbered contests (first, third, fifth,
  ...), and decreases by B in each of his even-numbered contests (second,
  fourth, sixth, ...).
  
  According to this estimate, after how many contests will he become Kaiden for
  the first time, or will he never become Kaiden?
samples: [{"input": "4000 2000 500", "output": "5\n    \n\nEach time Hikuhashi participates in a contest, his rating is estimated to\nchange as 0 \u2192 2000 \u2192 1500 \u2192 3500 \u2192 3000 \u2192 5000 \u2192 \u2026 After his fifth contest,\nhis rating will reach 4000 or higher for the first time.\n\n* * *"}, {"input": "4000 500 2000", "output": "-1\n    \n\nEach time Hikuhashi participates in a contest, his rating is estimated to\nchange as 0 \u2192 500 \u2192 -1500 \u2192 -1000 \u2192 -3000 \u2192 -2500 \u2192 \u2026 He will never become\nKaiden.\n\n* * *"}, {"input": "1000000000000000000 2 1", "output": "1999999999999999997\n    \n\nThe input and output values may not fit into 32-bit integers."}]