/******************************************************************************
 * This program the std. dev. of a list of float values on STDIN.
 * 
 * Copyright © 2017 Richard Lesh.  All rights reserved.
 *****************************************************************************/

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import org.pureprogrammer.Utils;

public class StandardDeviation {

    public static void main(String[] args) {
        String line;
        double total = 0;
        List<Double> samples = new ArrayList<>();

        while ((line = Utils.getline()) != null) {
            double d = Utils.stodWithDefault(line, 0.0);
            samples.add(d);
            total += d;
        }
        final int COUNT = samples.size();
        if (COUNT > 0) {
            final double AVERAGE = total / COUNT;
            double deviation = 0.0;
            for (double sample : samples) {
                deviation += Math.pow(sample - AVERAGE, 2.0);
            }
            System.out.println(Utils.format("{0:.16g}", Math.sqrt(deviation / COUNT)));
        }
    }
}