#include <iostream>

using namespace std;

class Cell
{
public:
    double val;
    Cell* next;
    Cell* prev;
    Cell(double v)
    {
        val = v;
        next = NULL;
        prev = NULL;
    }
};

class List
{
private:
    Cell* head = NULL;
    Cell* tail = NULL;
public:

    Cell* begin(){
      return head;
    }

    Cell* end(){
      return tail;
    }

    void push_front(double v)
    {
        if (head == NULL)
        {
            head = new Cell(v);
            tail = head;
        }
        else
        {
            Cell* n = new Cell(v);
            n->next = head;
            head->prev = n;
            head = n;
        }
    }

    void push_back( double v )
    {
        if( head == NULL ){
            head = new Cell(v);
            tail = head;
        }
        else
        {
            Cell* n = new Cell(v);
            n->prev = tail;
            tail->next = n;
            tail = n;
        }
    }


    void remove( int index ){
        Cell* elem = head;
        for( int i = 0; i < index; i++ ){
            elem = elem->next;
        }
        elem->prev->next = elem->next;
        elem->next->prev = elem->prev;
    }

    int find( double elem ){
        Cell* curr = head;
        int i = 0;
        while (curr != NULL)
        {
            if( curr->val == elem ){
              return i;
            }
            curr = curr->next;
            i++;
        }
        return -1;
    }

    void print()
    {
        Cell* curr = head;
        while (curr != NULL)
        {
            cout << curr->val << " ";
            curr = curr->next;
        }
        cout << endl;
    }
};

int main()
{

    int n;
    cout << "Enert n: ";
    cin >> n;

    if( n >= 2 ){

        List data;

        for( int i = 0; i < n; i++ ){

            double elem;
            cout << "Enter " << i + 1 << " element: ";
            cin >> elem;
            data.push_back(elem);

        }

        double ans = 1;
        Cell* start = data.begin();
        Cell* end   = data.end();
        for( int i = 0; i < n; i++ ){
            double elem;
            elem = start->val * end->val;
            start = start->next;
            end = end->prev;
            ans = ans * elem;
        }

        cout << "Answer is " << ans << endl;
    }else{
        cout << "ERROR: n is too small" << endl;
    }

    return 0;
}