#!/usr/bin/env tclsh9.0

set lefts [list]
set rights [list]

foreach line [split [read stdin] \n] {
    if {$line eq ""} continue
    lassign $line l r
    lappend lefts $l
    lappend rights $r
}

set lefts [lsort -integer $lefts]
set rights [lsort -integer $rights]

set total 0
for {set i 0} {$i < [llength $lefts]} {incr i} {
    set l [lindex $lefts $i]
    set r [lindex $rights $i]
    set d [expr {abs($l - $r)}]
    incr total $d
}

puts $total