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

int main() {
	for( ;; ) {
		int n;
		cin >> n;

		if( n == 0 ) {
			break;
		}

		vector<int> s( n );
		double m = 0;

		for( auto& v: s ) {
			cin >> v;
			m += v;
		}

		m /= n;

		double a = 0;
		for( int i = 0; i < n; ++i ) {
			a += pow( s.at( i ) - m, 2 );
		}

		cout << fixed << setprecision( 10 );
		cout << sqrt( a / n ) << endl;
	}
}

