//
// Created by 刘宇韬 on 2022年3月30日.
//
/**
 * @author 大菜狗
 */
#include "bits/stdc++.h"
using namespace std;
typedef long long LL;
typedef pair<int, int> PII;
#define pb push_back
#define fi first
#define se second
const int N = 500010;
int a[N];
int n;
long double sum;
int main() {
 std::ios::sync_with_stdio(false);
 cin >> n >> sum;
 long double avg = sum*1.0 / n;
 int clow = 0,low = 0;
 double ls = 0;
 for (int i = 0; i < n; i++) {
 cin >> a[i];
 }
 sort(a,a+n);

 long double res = 0;
 long double newAvg = avg;
 for (int i = 0; i < n; i++) {
 if (a[i]<=newAvg){
 sum-=a[i];
 res+=pow(avg-a[i],2);
 newAvg = sum*1.0/(n-i-1);
 }else{
 res+=pow(newAvg-avg,2);
 }
 }
 printf("%.4lf", sqrt(res/n));
}