#include <stdio.h>

int main(void)
{
        int n,i,j;
        double a,b,c;
        while(scanf("%d",&n) != EOF)
        {
                if(n == 0)
                {
                        printf("0.00\n");
                        continue;
                }
                else
                {
                        double sum = 0;
                        scanf("%lf%lf",&a,&b);
                        j = n;
                        while(j--)
                        {
                                scanf("%lf",&c);
                                sum += c;
                        }
                        printf("%.2lf\n",(b + n * a)/(n + 1) - sum);
                }
        }
        return 0;
}