#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
using namespace std;
const int N = 5e5 + 5;

double arr[N], avg, res;

int main()
{
    int n, m;
    scanf("%d %d", &n, &m);
    for (int i = 0; i < n; ++i)
        scanf("%lf", &arr[i]);

    sort(arr, arr+n);

    int idx = 0;
    double avg = m * 1.0 / n;
    double shouldPay = avg;
    while (idx < n && arr[idx] < shouldPay)
    {
       // cout << shouldPay << endl;
        res += pow(arr[idx]-avg, 2);
        m -= arr[idx];
        shouldPay = m * 1.0 / (n - (++idx));
    }

    res += (n - idx) * pow(shouldPay - avg, 2);
    res = sqrt(res / n);
    printf("%.4lf", res);
    return 0; 
}