#include <bits/stdc++.h>
using namespace std;

int main(){
    cout << fixed << setprecision(5);
    double n,s;
    cin >> n;
    while(n != 0){
    double sum = 0,psum = 0;
    for (int i = 0; i < n; i++)
    {
        cin >> s;
        sum += s;
        psum += s*s;
    }
    cout << sqrt(psum/n - sum*sum/n/n) << endl;
    cin >> n;
    }
    return 0;
}
