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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
int main()
{
    int a,b,h;
    int r;
    scanf("%d",&a);
    scanf("%d",&b);
    scanf("%d",&h);
    r = (a+b)*(h/2);

    if(a==b && b==h && a==h)
    {
        printf("\n%d\n",r);
        printf("In this case, a parallelogram is given, which is also a trapezoid.\n");

    }
    else
    {
         printf("\n%d\n",r);
         printf("When the lengths of the upper base, lower base, and height are %d,%d,and %d,respectively,the area of the trapezoid is (%d+%d)*%d/2=%d\n",a,b,h,a,b,h,r);

    }


}