PROBLEM STATEMENT
Little Johnny is in the first grade and just found out about addition.  He quickly learned the 
addition table and is becoming bored in class, so he thinks of a game.  The game consists of 
choosing an integer and summing its digits.  If the result is a single digit, the game ends.  
Otherwise, Johnny repeats the process on the result until he gets a single digit.

For example, if Johnny starts with the number 12345, he will add the digits 1 + 2 + 3 + 4 + 5 to 
get 15.  The result is not a single digit, so he will repeat the process to get 1 + 5 = 6.  The 
new result is a single digit, so the game ends.

Johnny is curious to see if his computations are correct, so he asks you what the final result is 
for the number n.

DEFINITION
Class:DigitsSum
Method:lastDigit
Parameters:int
Returns:int
Method signature:int lastDigit(int n)


CONSTRAINTS
-n will be between 0 and 2147483647, inclusive.


EXAMPLES

0)
12345

Returns: 6

The example in the problem statement.

1)
6

Returns: 6

In this simple example, the sum of the digits is 6, so the game ends after just one step.

2)
999999999

Returns: 9

The sum of the digits is 9 + 9 + 9 + 9 + 9 + 9 + 9 + 9 + 9 = 81.  The process is repeated once 
more to get 8 + 1 = 9, which is a single digit.

3)
213413512

Returns: 4



4)
314

Returns: 8



5)
2147483647

Returns: 1



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