use List::Util qw(max);

use strict;
use warnings;

my %vals;

# Put Data into a Hash of Arrays
while (<DATA>) {
	chomp;
	my ($key, $val) = split;
	push @{$vals{$key}}, $val;
}

for my $key (sort {$a <=> $b} keys %vals) {
	my $max = max @{$vals{$key}};
	print "$key $max\n";
}

=prints
1 4
2 7
3 10
=cut

__DATA__
1  3
1  2
1  4
2  5
2  7 
3  10
3  0