$n=<>;
@a=glob<>;
$d=$_-($n-1)/2,$s+=$a[$_],$t+=$a[$_]*$d,$u+=$d*$d for 0..$n-1;
$a=$t/$u;
$b=$s/$n-$a*($n-1)/2;
$c+=($a*$_+$b-$a[$_])**2 for 0..$n-1;
print$b,$",$a,$/,$c;