#include <bits/stdc++.h>
using namespace std;
int main(){
	int n;
	double a[1010], avg, ans;
	while(cin >> n){
		if(n==0)
			break;
		avg = ans = 0;
		for(int i=1; i<=n; i++){
			cin >> a[i];
			avg += a[i];
		}
		avg = 1.0*avg/n;
		for(int i=1; i<=n; i++)
			ans += 1.0*(avg-a[i])*(avg-a[i]);
		ans = sqrt(ans/n);
		cout << fixed << setprecision(5) << ans << endl;
	} 
	return 0;
}
