#include <stdio.h>

struct list {
   float val;
   list* next;
   list* prev;
};

list* input(FILE* fp)
{
   list* temp = new list;
   float c;
   fscanf_s(fp, "%f", &c);
   temp->val = c;
   list* head = temp;
   while (fscanf_s(fp,"%f", &c) != EOF)
   {
      temp->next = new list;
      temp->next->prev = temp;
      temp->next->val = c;
      temp = temp->next;
   }
   temp->next = head;
   head->prev = temp;
   return(head);
}

float prod(list* left, list* right, list* head)
{
   float a = 1;
   a = a * (right->val + left->val);
   right = right->prev;
   left = left->next;
   while (left != head)
   {
      a = a * (right->val + left->val);
      right = right->prev;
      left = left->next;
   }
   return a;
}

int main()
{
   FILE *fp;
   if (fp = fopen("input.txt", "r"))
   {
      list* head = input(fp);
      list* temp_l = head;
      list* temp_r = head->prev;
      float result = prod(temp_l, temp_r, head);
      printf("%f", result);
   }

   return 0;
}