Given a string S consisting of only uppercase and lowercase characters. The task is to sort uppercase and lowercase letters separately such that if the i_th place in the original string had an Uppercase character then it should not have a lowercase character after being sorted and vice versa.

Example 1:

Input:
N = 12
S = defRTSersUXI
Output: deeIRSfrsTUX
Explanation: Sorted form of given string
with the same case of character as that
in original string is deeIRSfrsTUX

Example 2:

Input:
N = 6
S = srbDKi
Output: birDKs
Explanation: Sorted form of given string
with the same case of character will
result in output as birDKs.

Your Task:
You only need to complete the function caseSort that takes a string str and length of the string n and returns sorted string.

Expected Time Complexity: O(Nlog(N)).
Expected Auxiliary Space: O(N).

Constraints:
1 ≤ N ≤ 10⁵