import std.stdio, std.string, std.conv, std.algorithm, std.array, std.math;
void main(){
	while(1){
		auto n = readln.chomp.to!int;
		if(n==0) break;
		int sum;
		real ans=0;
		auto s = readln.split.map!(to!int);
		for(int i;i<n;++i)
			sum += s[i];
		real ave =sum/cast(real)n;
		for(int i;i<n;++i)
			ans += (s[i]-ave)^^2;
		writefln("%.5f",sqrt(ans/n));
	}
}