trapec

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

    }
}