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

void main() {
  foreach (string line; lines(stdin)) {
    if (line == "0\n")
      break;

    int n = line.chomp.to!int;
    auto points = readln.chomp.split.map!(to!double);
    auto avr = points.reduce!"a+b" / n;
    double var = 0;
    foreach (e; points) { var += pow(avr - e, 2); }
    printf("%.8lf\n", sqrt(var / n));
  }
}