How to virutal destructor will delete the derived class memory

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C++

Program:

//============================================================================
// Name        : revision6.cpp
// Author      : 
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
using namespace std;

class innova {
public:
	innova() {
		cout << "innova constructor called" << endl;
	}
	virtual void speed() {
		cout << "The speed of innova is: 160kmph" << endl;
	}

	virtual ~innova() {
		cout << "innova destructor called" << endl;
	}
};

class nano : public innova {
public:
	nano() {
		cout << "nano constructor called" << endl;
	}
	void speed() {
		cout << "The speed of nano is: 60kmph" << endl;
	}
	~nano() {
		cout << "Nano destructor called" << endl;
	}
};
int main() {
	innova *inobj = new nano;
	inobj->speed();
	delete inobj; 
	return 0;
}

Output:

innova constructor called
nano constructor called
The speed of nano is: 60kmph
Nano destructor called
innova destructor called

My question:
In main function I am deleting the innova pointer (delete inobj), Here its calling the both class destructor , i dont how it is calling internally using virtual destructor.

Could you please clarify this problem.

Thanks in advance
Paramaraj