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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
 

//     String[] nyu=sc.nextLine().split(" ");

     String nyu=sc.nextLine();
//int A=Integer.parseInt(nyu[0]);
//int B=Integer.parseInt(nyu[1]);
//int C=Integer.parseInt(nyu[2]);
int D=Integer.parseInt(nyu);
nyu=sc.nextLine();
int E=Integer.parseInt(nyu);
nyu=sc.nextLine();
int F=Integer.parseInt(nyu);



//StringBuffer sb = new StringBuffer(nyu);
//		String dst = sb.reverse().toString();

//     String nyu2=sc.nextLine();
//int E=Integer.parseInt(nyu2);



//double A=Double.parseDouble(nyu[0]);
//double B=Double.parseDouble(nyu[1]);
/*
switch(nyu){
case "H H":
System.out.println("H") ;
break;

case "D D":
System.out.println("H") ;
break;

case "H D":
System.out.println("D") ;
break;

case "D H":
System.out.println("D") ;
break;


default:
System.out.println("NO") ;

break;
}
*/

//int res=Math.min((A*B),C);

//for(String tem:bo){
//if(tem.equals(nyu))res="vowel";
//}
//int res=0;
//for(int i=0;i<300;i++){
//if(num[i]==1)res=i;
//}

//char[] c = nyu.toCharArray();


//System.out.println(nyu+"-"+line_r_2+"-"+nyu2+"-"+line_r_1);



//if(A+B==C || B+C==A || C+A==B){
//double res=Math.ceil((AB)/2);

//System.out.println("Yes");
//}else if(B<A){
//System.out.println("Alice");

//}else{
System.out.println((D+E)*F / 2);
//}




	}
}