Problem:
Score : 100 points

Problem Statement

You are given a trapezoid. The lengths of its upper base, lower base, and height are a, b, and h, respectively.

An example of a trapezoid

Find the area of this trapezoid.

Constraints

1≦a≦100

1≦b≦100

1≦h≦100

All input values are integers.

h is even.

Input

The input is given from Standard Input in the following format:

a
b
h

Output

Print the area of the given trapezoid. It is guaranteed that the area is an integer.

Sample Input 1

3
4
2

Sample Output 1

7

When the lengths of the upper base, lower base, and height are 3, 4, and 2, respectively, the area of the trapezoid is (3+4)×2/2 = 7.

Sample Input 2

4
4
4

Sample Output 2

16

In this case, a parallelogram is given, which is also a trapezoid.

Solution in Scala (2.11.7) (judge verdict: Accepted)

import scala.math._

object Main extends App {

  val YES = "YES"
  val Yes = "Yes"
  val NO = "NO"
  val No = "No"
  ///////////////////////////////////////////

  val sc = new java.util.Scanner(System.in)
  val a = sc.nextInt
  val b = sc.nextInt
  val h = sc.nextInt
//  val list = List.fill(3)(sc.nextInt)

  val ans = (a + b) * h / 2

  println(ans)


  ///////////////////////////////////////////

  def bigIterator(start: BigInt, end: BigInt, step: BigInt = 1) =
    Iterator.iterate(start)(_ + step).takeWhile(_ <= end)

  def lcm(a :Int, b :Int): Int =
    a / gcd(a, b) * b

  def lcm(a :Long, b :Long): Long =
    a / gcd(a, b) * b

  def gcd(a: Int, b: Int): Int =
    if (b == 0) a else gcd(b, a % b)

  def gcd(a: Long, b: Long): Long =
    if (b == 0) a else gcd(b, a % b)

  def setOrUpdated[A, B](a: Map[A, B], key: A, value: B, f: (B, B) => B) =
    a.get(key) match {
      case Some(v) => a.updated(key, f(value, v))
      case _ => a + (key -> value)
    }
}