powersOfTwo

Mr. Privalov has a number k and an array of n elements, each element of which is the power of 2 and doesn’t exceed 2k. All powers from 20 to 2k are appear in the array (maybe even more than once) except one, which Mr. Privalov wants to find.

Your task is help to Mr.Privalov to find a missed power.

Example

• For k = 1 and arr = [1, 1], the output should be powersOfTwo(k, arr) = 2;
• For k = 3 and arr = [8, 4, 2], the output should be powersOfTwo(k, arr) = 1

Input/Output

• [execution time limit] 0.5 seconds

• [input] integer k
  

  The maximum power of two.
  Constraints:
  1 ≤ k ≤ 30.

• [input] array.integer arr

  Array of powers of two. It is guaranteed that the length of the array is n, all its elements are powers of two not greater than 2k, and there is exactly one missing power in it.
  
  Constraints:
  1 ≤ arr.length ≤ 100.

• [output] integer

  • The missing power.