Sample Input

Sample Output

6.000000

52.833333

 #include<stdio.h>

 #include<string.h>

 #include<math.h>

 #include<queue>

 #include<algorithm>

 #include<time.h>

 using namespace std;

 const int maxn = ;

 const int N=;

 #define lson rt<<1///rt*2

 #define rson rt<<1|1///rt*2+1

 int main()

 {

     int n,i;

     int a[];

     while(scanf("%d", &n) != EOF)

     {

         int sum=;

         for(i=;i<=n;i++)

         scanf("%d", &a[i]);

         if(n==)

             printf("%lf\n",1.0*a[]);

         else if(n==)

             printf("%lf\n",1.0*(a[]+a[])/);

         else

         {

             for(i=;i<n;i++)

                 sum+=a[i];

             int x=a[]+a[n];

             printf("%lf\n", 1.0*x/+1.0*sum/);

         }

     }

     return ;

 }