Problem:
Score : 200 points

Problem Statement

Snuke has N integers. Among them, the smallest is A, and the largest is B.
We are interested in the sum of those N integers. How many different possible sums there are?

Constraints

1 ≤ N,A,B ≤ 10^9

A and B are integers.

Input

Input is given from Standard Input in the following format:

N A B

Output

Print the number of the different possible sums.

Sample Input 1

4 4 6

Sample Output 1

5

There are five possible sums: 18=4+4+4+6, 19=4+4+5+6, 20=4+5+5+6, 21=4+5+6+6 and 22=4+6+6+6.

Sample Input 2

5 4 3

Sample Output 2

0

Sample Input 3

1 7 10

Sample Output 3

0

Sample Input 4

1 3 3

Sample Output 4

1

Solution in Haskell (GHC 7.10.3) (judge verdict: Wrong Answer)

import Control.Applicative( (<$>))

main = do
    [n_, a_, b_] <- map (read::String->Integer) . words <$> getLine
    let
	combi n r = let
			numerator = product [n-r+1..n]
			denominator = product [1..r]
		    in
			numerator `quot` denominator

    print $ if a_>b_ || (a_<b_&&n_==1)
		then 0
		else combi (b_-a_+n_-2) (n_-2)