1001 A+B Format (20)（20 分）
Calculate a + b and output the sum in standard format -- that is, the
digits must be separated into groups of three by commas (unless there
are less than four digits).
Input
Each input file contains one test case. Each case contains a pair of
integers a and b where -1000000 <= a, b <= 1000000. The numbers
are separated by a space.
Output
For each test case, you should output the sum of a and b in one line.
The sum must be written in the standard format.
Sample Input
-1000000 9
Sample Output
-999,991
