#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#define ll long long
#define num ch-'0'
#define ld long double 
#define rep(i,a,b) for(register int i=(a);i<=(b);++i)
using namespace std;
const int N=500010;
ll cnt,n,m,a[N];
ld b[N],ans=0,avg,tot,nowavg;
inline void get(ll &res)
{
    char ch;bool flag=0;
    while(!isdigit(ch=getchar()))
        (ch=='-')&&(flag=true);
    for(res=num;isdigit(ch=getchar());res=res*10+num);
    (flag)&&(res=-res);
}
int main() 
{
    get(n),get(m);
    rep(i,1,n) get(a[i]);
    sort(a+1,a+n+1);
    nowavg=avg=1.0*m/n;
    tot=0;
    rep(i,1,n)
    {
        if(a[i]<nowavg)
        {
            ans+=(a[i]-avg)*(a[i]-avg);
            tot+=a[i];
        }
        else
        {
            nowavg=(m-tot)/(n-i+1);
            if(a[i]>=nowavg)
            {
                ans+=(nowavg-avg)*(nowavg-avg)*(n-i+1);
                break;
            }
            --i;
        }
    }
    ans/=(ld)n;
    ans=sqrt(ans);
    printf("%.4Lf",(ld)ans);
    return 0;
}