struct Square {                     struct Rectangele 
                                    : Square {
    float a;                          //float a
                                        float b;
    float perimeter() {                 float perimeter() {
         return a * 4                       return (a + b) * 2
    }                                   }
    float area() {                      float area() {
         return a * a                       return a * b;
    }                                   }          
}                                   }

struct Diamond
: Square {
    float angle;
    
    float area() {
        return a * a / 2;
    }
}

struct Parallelogram
: Diamond , Rectangele {
    //...
}