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



var sc = bufio.NewScanner(os.Stdin)

func nextLine() string {
    sc.Scan()
    return sc.Text()
}

func main() {
    line := nextLine()
    a, _ := strconv.Atoi(line)
    line = nextLine()
    b, _ := strconv.Atoi(line)
    line = nextLine()
    h, _ := strconv.Atoi(line)

    area := float64 ((a + b) * h) / 2
    fmt.Print(area)
}