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 Go (1.6) (judge verdict: Accepted)

package main

import(
	"fmt"
  	"bufio"
  	"os"
	"strconv"
)

var sc = bufio.NewScanner(os.Stdin)

func nextLine() int{
  sc.Scan()
  i, _:= strconv.Atoi(sc.Text())
  return i
}

func main(){
  a,b,h := nextLine(),nextLine(),nextLine()
  var total = 0
  if a==b && b == h && a == h{
  	total = b*h
  }else{    
    total = (a + b)*h/2
  }
  fmt.Println(total)
}