阅读以下程序，写出输出结果。
class A {
double f(double x, double y) {
return x * y;
}
}
class B extends A {
double f(double x, double y) {
return x + y;
}
}
public class Test {
public static void main(String args[]) {
B obj = new B();
System.out.println("The program output is " + obj.f(6, 7));
}
}
