#!/usr/bin/perl
#

$line = <STDIN>;
@words = split(/\s+/, " " . $line);
$v1 = $words[1];
$s1 = $words[2];
$line = <STDIN>;
@words = split(/\s+/, " " . $line);
$v2 = $words[1];
$s2 = $words[2];
$dt = 0.5;

$avg_vel = ($v2 - $v1) / $dt;
$max_vel = (  ($v2 + $s2) - ($v1 - $s1) ) / $dt;
$min_vel = (  ($v2 - $s2) - ($v1 + $s1) ) / $dt;
$uncert = ($max_vel - $min_vel) / 2.0;

printf "  avg %6.2f  +/-  %6.2f  \n", $avg_vel, $uncert;


exit 0;