/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{    
		 Scanner in=new Scanner(System.in);	
		 int n;
         n=in.nextInt();
         double[] x= new double[n];
         for (int i=0; i<n; i++)//вводим массив
         x[i]=in.nextInt();
         double p=1;  
         for (int i=0; i<n-2; i++)//подсчитываем необходимое произведение
        {
          p*=(x[i]+2*x[i+1]+x[i+2]);
        }
        System.out.print(p);
	}
}

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OSAxIDIgMCAxIDIgMCAxIDIgMA==

9 1 2 0 1 2 0 1 2 0