import java.util.Scanner;

public class Project {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double b1 = Double.parseDouble(sc.nextLine());
        double b2 = Double.parseDouble(sc.nextLine());
        double h = Double.parseDouble(sc.nextLine());

        double result = (b1 + b2) + h / 2;
        System.out.printf("pp result is %.2f", result );
    }
}