use strict;
use Data::Dump qw/dump/;

my %data;

while (<DATA>) {
    chomp;
    my ( $field1, $field2, $field3, $field4 ) = split '\s+';
    $data{$field1}{$field2}{'min'} = $field3
        if ( not defined $data{$field1}{$field2}{'min'}
        or $field3 < $data{$field1}{$field2}{'min'} );
    $data{$field1}{$field2}{'max'} = $field4
        if ( not defined $data{$field1}{$field2}{'max'}
        or $field4 > $data{$field1}{$field2}{'max'} );
} ## end while (<DATA>)
print dump( \%data );

__DATA__
253868	20	317	2628
253868	20	317	7294
256158	9	329	371
256158	9	329	86450
728481	1	353	1361
154664	7	440	449688
154664	7	440	563


##</code><code>##

{
  154664 => {  7 => { max => 449688, min => 440 } },
  253868 => { 20 => { max =>   7294, min => 317 } },
  256158 => {  9 => { max =>  86450, min => 329 } },
  728481 => {  1 => { max =>   1361, min => 353 } },
}