title: T 103 - Negative Marking
body: <p>Raju is giving his JEE Main exam. The exam has Q questions and Raju needs S marks to pass. Giving the correct answer to a question awards the student with 4 marks whereas giving the incorrect answer to a question awards the student with negative 3 (-3) marks. If a student chooses to not answer a question at all, he is awarded 0 marks.</p>
  
  <p>Write a program to calculate the minimum accuracy that Raju will need in order to pass the exam.</p>
  
  <p>Input
  Input consists of multiple test cases.
  Each test case consists of two integers Q and S</p>
  
  <p>Output
  Print the minimum accuracy upto 2 decimal places
  Print -1 if it is impossible to pass the exam</p>
  
  <p>Sample Input 0</p>
  
  <p>2</p>
  
  <p>10 40</p>
  
  <p>10 33</p>
  
  <p>Sample Output 0</p>
  
  <p>100.00</p>
  
  <p>90.00</p>