trapeze

import java.util.Scanner;
public class Трапец {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		System.out.print("a = ");
		double a = scan.nextInt();
		System.out.print("b = ");
		double b = scan.nextInt();
		System.out.print("h = ");
		double h = scan.nextInt();
        double S = ((a + b)*h) / 2;
        System.out.print("S = " + S + "square cm");

	}

}