#351 ScicomLoveBug

Statement

Statement language

The original title of this problem was ScicomLove. However, because of lovebugs, the angry problem setter changed the title to ScicomLoveBug!

There are currently $N$ lovebugs in the club room. While summer continues, the number of lovebugs increases by $A$ every day.

Find the expected number of lovebugs in the club room after $D$ days.

The input is given in the following format.

$N\ A\ D$

Print the expected number of lovebugs in the club room after $D$ days.

#	Score	Constraints
1	43	$1 \leq D \leq 1000$ .
2	57	There are no additional constraints.

Sample 1

Input

5 3 4

Output

17

Sample 2

Input

1000000000 1000000000 1000000000

Output

1000000001000000000