+ import std.math;
  import std.typecons;
- import std.math;
  /*
  In this problem, you will implement a function that takes two arrays of numbers,
-     and determines whether it is possible to perform an exchange of elements
? ----

+ and determines whether it is possible to perform an exchange of elements
-     between them to make lst1 an array of only even numbers.
? ----

+ between them to make lst1 an array of only even numbers.
-     There is no limit on the number of exchanged elements between lst1 and lst2.
? ----

+ There is no limit on the number of exchanged elements between lst1 and lst2.
-     If it is possible to exchange elements between the lst1 and lst2 to make
? ----

+ If it is possible to exchange elements between the lst1 and lst2 to make
-     all the elements of lst1 to be even, return "YES".
? ----

+ all the elements of lst1 to be even, return "YES".
-     Otherwise, return "NO".
? ----

+ Otherwise, return "NO".
-     For example:
? ----

+ For example:
-     >>> exchange([1L, 2L, 3L, 4L], [1L, 2L, 3L, 4L])
? ----

+ >>> exchange([1L, 2L, 3L, 4L], [1L, 2L, 3L, 4L])
-     "YES"
+ "YES"
-     >>> exchange([1L, 2L, 3L, 4L], [1L, 5L, 3L, 4L])
? ----

+ >>> exchange([1L, 2L, 3L, 4L], [1L, 5L, 3L, 4L])
-     "NO"
+ "NO"
-     It is assumed that the input arrays will be non-empty.
? ----

+ It is assumed that the input arrays will be non-empty.
-     
  */
  string exchange(long[] lst1, long[] lst2)