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

int main() {
	int N;
	double S[1000], sum, m;
	while (1) {
		sum = 0;
		cin >> N;
		if (N == 0) break;
		for (int i = 0; i < N; i++) {
			cin >> S[i];
			sum += S[i];
		}
		m = sum / N;
		sum = 0;
		for (int i = 0; i < N; i++) {
			sum += (S[i] - m) * (S[i] - m);
		}
		printf("%.8f\n", sqrt(sum / N));
	}
}
