PROBLEM STATEMENT

A multifactorial of a number is a generalization of the factorial function. The k-multifactorial 
of n is denoted by fack(n). The k-multifactorial of n is the product of every positive number of the
form n - X*k, where X is a non-negative integer. For example, the 3-multifactorial of 14 
is 14*11*8*5*2 = 12320, and the 4-multifactorial of 5 is 5*1 = 5.

A formal definition of multifactorial is:

fack(n) = n if k >= n 
fack(n) = n*fack(n-k) if k < n 


You will be given n and k and have to return the value of fack(n) as a string with no leading 
zeroes (this value is always a positive integer). If fack(n) is strictly greater than 
1000000000000000000 (1018), return "overflow" (quotes for clarity) instead.


DEFINITION
Class:Multifactorial
Method:calcMultiFact
Parameters:int, int
Returns:string
Method signature:string calcMultiFact(int n, int k)


NOTES
-1000000000000000000 (1018) fits in a long long.


CONSTRAINTS
-n and k will each be between 1 and 2000000000 (2*109), inclusive.


EXAMPLES

0)
14
3

Returns: "12320"

The first example in the problem statement.

1)
5
4

Returns: "5"

The second example in the problem statement.

2)
1000
2

Returns: "overflow"

Way too big!

3)
2000000000
1900000000

Returns: "200000000000000000"



4)
1000
256

Returns: "84232704000"



5)
2000000000
1

Returns: "overflow"



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