#inclde<iostream>
#include<string>
#include<iomanip>
using namespace std;
class fuel{
    protected:
      float quantity;
      float price;
    public;
      fuel(float q, float p) : quantity(q) , price p{}
      virtual void calculatecost()=0;
};
class petrol : public fuel{
public:
    petrol(float q , float p): fuel(q,p){}
    void calculatecost() override{
        if(quantity<0 || price<0){
            cour<<"Invalid input"<<endl;
        }else{
            float totalcost=quantity * price;
            cout<<fixed<<setprecision(2)<<totalcost<<endl;
        }
    }
};