Decode the string encoded with the given algorithm

Given a decoded string str which was decoded with the following encoding algorithm: 
Write down the middle character of the string then delete it and repeat the process until there are no characters left. For example, "abba" will be encoded as "bbaa". 
Note that the middle character is the first character of the two middle characters when the length of the string is even.
Examples:

Input: "ofrsgkeeeekgs"
Output: geeksforgeeks

Input: str = "bbaa"
Output: abba

Approach: It can be observed that while decoding the string, the first letter of the encoded string becomes the median of the decoded string. So first, write the very first character of the encoded string and remove it from the encoded string then start adding the first character of the encoded string first to the left and then to the right of the decoded string and do this task repeatedly till the encoded string becomes empty.
For example: 

Encoded String Decoded String
ofrsgkeeeekgs o
frsgkeeeekgs fo
rsgkeeeekgs for
sgkeeeekgs sfor
gkeeeekgs sforg
keeeekgs ksforg
eeeekgs ksforge
eeekgs eksforge
eekgs eksforgee
ekgs eeksforgee
kgs eeksforgeek
gs geeksgorgeek
s geeksforgeeks 

Below is the implementation of the above approach: 
 

geeksforgeeks

The Complexity: O(n)