#!/usr/bin/perl -w
use strict;
my @stddev;
while( <DATA> ){
  my @fields = split ' ', $_;
  my $N = scalar(@fields);
  my $sum = 0;
  $sum += $_ for @fields;
  my $mean = $sum / $N;
  $sum = 0;
  $sum += ($_ - $mean)**2 for @fields;
  push @stddev, sqrt($sum/$N);
}
print map {"$_\n"} @stddev;

__DATA__
1.8 2.5 3.8 1.9 -3.5 -3.5 3.2 -3.9 4.2 4.5 2.8
-1.3 -0.9 -0.7 -0.4 -0.8 -3.5 -3.5 -1.6 -4.5