#include <iostream>#include <cstdio>#include <cmath>#include <algorithm>#include <cstring>using namespace std;double dp[20005];int ci[125];double is=0.5*(1+sqrt(5));int main(){	int n,f,ma;	while(scanf("%d%d",&n,&f)!=EOF){		ma=-1;		for(int i=1;i<=n;i++){			scanf("%d",&ci[i]);			ma=max(ma,ci[i]);		}		ma=ma*2;		for(int i=max(ma,f);i>=f;i--){			dp[i]=0;			for(int k=1;k<=n;k++){				if(i>ci[k]) dp[i]+=(int)(is*ci[k]*ci[k]);				else{					dp[i]+=(dp[i+ci[k]]+1);				}			}			dp[i]=(dp[i])/n;		}		printf("%.3lf\n",dp[f]);	}	return 0;}