Adding Commas

Large numbers are much easier to read when a comma is inserted every three digits. For example, 153920529 can be written as 153,920,529.

Given an integer $N$, write a program that inserts a comma every three digits, counting from the right, and prints the result.

The first line contains an integer $N$ ($1 \le N \le 2{,}000{,}000{,}000$).

Print $N$ on a single line with a comma separating every group of three digits, counting from the right. The leftmost group has no leading comma.