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"
)

func main(){
    
    a := nextInt()
    b := nextInt()
    h := nextInt()
    
	fmt.Println((a+b)*h/2)
}
 
/* templates */


func Max(a []int) int {
    r := a[0]
    for i := 0; i < len(a); i++ {
        if r < a[i] {
            r = a[i]
        }
    }
    return r
}
 
func Min(a []int) int {
    r := a[0]
    for i := 0; i < len(a); i++ {
        if r > a[i] {
            r = a[i]
        }
    }
    return r
}
 
func Sum(a []int) (r int) {
    for i := range a {
        r += a[i]
    }
    return r
}
 
func Abs(a float64) float64 {
    if a < 0 {
        return -a
    }
    return a
}
 
type Pair struct {
    a, b int
}
 
type Pairs []Pair
 
func (p Pairs) Len() int {
    return len(p)
}
 
func (p Pairs) Swap(i, j int) {
    p[i], p[j] = p[j], p[i]
}
 
func (p Pairs) Less(i, j int) bool {
    return p[i].b < p[j].b
}
 
var nextReader func() string
 
func init() {
    nextReader = NewScanner()
}
 
func NewScanner() func() string {
    r := bufio.NewScanner(os.Stdin)
    r.Buffer(make([]byte, 1024), int(1e+11))
    r.Split(bufio.ScanWords)
    return func() string {
        r.Scan()
        return r.Text()
    }
}

func nextString() string {
    return nextReader()
}
 
func nextInt64() int64 {
    v, _ := strconv.ParseInt(nextReader(), 10, 64)
    return v
}
 
func nextInt() int {
    v, _ := strconv.Atoi(nextReader())
    return v
}
 
func nextInts(n int) []int {
    r := make([]int, n)
    for i := 0; i < n; i++ {
        r[i] = nextInt()
    }
    return r
}

func nextStrings(n int) []string {
    r := make([]string, n)
    for i := 0; i < n; i++ {
        r[i] = nextString()
    }
    return r
}

func nextFloat64() float64 {
    f, _ := strconv.ParseFloat(nextReader(), 64)
    return f
}