重要的是从小到大枚举，每当一个人交钱后，要更新剩下的平均值，这样才能使得标准差最小

#include<bits/stdc++.h>
using namespace std;
const int N = 5e5 + 10;
int n;
long double s;
int a[N];
int main()
{
    cin >> n >> s;
    long double avg;
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    avg = s / n;
    sort(a, a + n);
    double cnt;
    long double res=0;
    for (int i = 0; i < n; i++) {
        cnt = s / (n - i);
        if (a[i] < cnt)
            cnt = a[i];
        res += (cnt - avg) * (cnt - avg);
        s -= cnt;
    }
    printf("%.4Lf\n", sqrt(res / n));
    return 0;
}