题解好多都过不了啊（嘿嘿嘿）
实力通过

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define IOS ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
#define lowbit(x) (-x&x)
int qmi(int a,int b){int res = 1;while(b){if(b&1){res = res*a;}b = b>>1;a = a*a; } return res;}
const int N = 5e5+10;
long double s;
long double a[N];
int n;
void solve()
{
    cin>>n>>s; for(int i=1;i<=n;++i) cin>>a[i];
    sort(a+1,a+1+n);
    double aver = s/n;
    int i=1;
    long double left = 0;
    long double laver = 0;
   // cout<<aver<<endl;
    while(i<=n){
        if(a[i]<=aver){
            left += aver - a[i];
            i++;
        }else{
            laver = left / (n-i+1);
            if(a[i]-aver <= laver){
                left = left - (a[i]-aver);
            }else{
                break;
            }
            i++;
        }
    }
    long double ans = 0;
    for(int j=1;j<=n;++j){
        if(j<i){
            ans+=(a[j]-aver)*(a[j]-aver);
        }else{
            ans+=(aver+laver-aver)*(aver+laver-aver);
        }
    }
    ans = sqrt(ans/n);
    printf("%.4llf",ans);
}
signed main()
{
    //freopen("D:/vsCode/.vscode/oi/in.txt","r",stdin);
    //freopen("D:/vsCode/.vscode/oi/out.txt","w",stdout);
    IOS
    int t = 1;
    //cin>>t;
    while(t--) solve();
    system("pause");
    return 0;
}