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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;


public class Main {


    public static void main(String[] args) throws IOException {
        MyScanner scanner = new MyScanner();
        PrintStream out = System.out;

        Main main = new Main();

        int a = scanner.nextInt();
        int b = scanner.nextInt();
        int h = scanner.nextInt();

        out.println( ((a + b)*h)/2  );

        scanner.reader.close();
        out.close();
    }

    // -----------MyScanner class for faster input----------
    public static class MyScanner {
        BufferedReader reader;

        public MyScanner() {
            this.reader = new BufferedReader(new InputStreamReader(System.in));
        }

        public void close() throws IOException {
            this.reader.close();
        }

        int nextInt() {
            return Integer.parseInt(this.next());
        }

        long nextLong() {
            return Long.parseLong(this.next());
        }

        double nextDouble() {
            return Double.parseDouble(this.next());
        }

        String next() {
            String str = "";
            try {
                str = this.reader.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }

        String[] nextStringArray() {
            String[] str = null;
            try {
                str = this.reader.readLine().trim().split(" ");
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }

        int[] nextIntArray() {
            String[] data  = nextStringArray();
            int[] a  = new int[data.length];

            for (int i = 0; i < a.length; i++) {
                a[i] = Integer.parseInt(data[i]);
            }

            return a;
        }

        Integer[] nextIntegerArray() {
            String[] data  = nextStringArray();
            Integer[] a  = new Integer[data.length];

            for (int i = 0; i < a.length; i++) {
                a[i] = Integer.parseInt(data[i]);
            }

            return a;
        }

        long[] nextLongArray() {
            String[] data  = nextStringArray();
            long[] a  = new long[data.length];

            for (int i = 0; i < a.length; i++) {
                a[i] = Long.parseLong(data[i]);
            }

            return a;
        }
    }
}