import std.stdio, std.string, std.array, std.conv, std.math, std.algorithm;

void main() {
    while (true) {
        int n = readln.chomp.to!int;
        if (n == 0) break;
        double[] s = readln.chomp.split.to!(double[]);
        double m = s.sum / n;
        s[] -= m;
        double sigma = sqrt(s.map!(a => a ^^ 2).sum / n);
        writefln("%0.8f", sigma);
    }
}
