Adding Commas [Traditional, 2010]

Bessie is working with large numbers N (1 <= N <= 2,000,000,000) 
like 153920529 and realizes that the numbers would be a lot easier
to read with commas inserted every three digits (as is normally     
done in the USA; some countries prefer to use periods every three
digits). Thus, she would like to add commas: 153,920,529 .  Please
write a program that does this.

PROBLEM NAME: commas

INPUT FORMAT:

* Line 1: A single integer: N

SAMPLE INPUT (file commas.in):

153920529

OUTPUT FORMAT:

* Line 1: The integer N with commas inserted before each set of three
        digits except the first digits (as traditionally done in many
        cultures)

SAMPLE OUTPUT (file commas.out):

153,920,529