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: p,a,b = map(int,input().split())
  if(a<=b):
    print(-1)
  else:
    p-=a
    up=a-b
    if(p<=0):
      print(1)
    else
    	num=p//up+(p%up!=0)
    	print(num*2+1)
  
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."}]