#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

int main(){
	int n;
	double s[1000], ave = 0, a = 0;
	while(cin >> n && n != 0){
		ave = 0, a = 0;
		for(int i = 0; i < n; i++){
			cin >> s[i];
			ave += s[i];
		}
		ave /= n;
		for(int i = 0; i < n; i++){
			a += pow(s[i]-ave, 2);
		}
		a /= n;
		cout << fixed << setprecision(5) << sqrt(a) << endl;
	}
	return 0;
}
