import std.stdio, std.string, std.conv, std.algorithm, std.math;
void main() {
	for (;;) {
		auto n = readln.chomp.to!ulong;
		if (n == 0) break;
		ulong[] d = readln.split.to!(ulong[]);
		ulong s = d.reduce!"a + b";
		ulong av = s / n;
		real r = d.map!(a => (a - av).pow(2)).sum / n;
		"%.8f".writefln(r.sqrt);
	}
}