HDU 2086

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define max_v 3005
int main()
{
    //n=4  5A1=4A0+A5-8C1-6C2-4C3-2C4
    int n;
    double x,y;
    double c[max_v];
    while(~scanf("%d",&n))
    {
        scanf("%lf %lf",&x,&y);
        for(int i=1;i<=n;i++)
        {
            scanf("%lf",&c[i]);
        }
        int v=2;
        double sum=0;
        for(int i=n;i>=1;i--)
        {
            sum+=v*c[i];
            v+=2;
        }
        double result=(n*x+y-sum)/(n+1);
        printf("%0.2lf\n",result);
    }
    return 0;
}