Write a program sum that takes zero or more arguments. If at least one of the arguments is not an integer value, the program must print the message sum: invalid arguments to stderr and end with exit status 1. Otherwise, the program must print the sum of the integer arguments to stdout and end with exit status 0.

Example

$ python ./sum
0
$ python ./sum 1 2 3 4 5 6 7 8 9 10
55
$ python ./sum 1 -2 3 -4 5 -6 7 -8 9 -10
-5
$ python ./sum a b c
sum: invalid arguments
$ echo $?
1