#!/usr/bin/perl -w

use strict;
use warnings;

my %hash;
while (<DATA>) {
    my ($coord, $dist) = split;
    $hash{$coord} = $dist 
        unless defined $hash{$coord} && $dist > $hash{$coord};
}

print "$_\t$hash{$_}\n" foreach (sort { $a <=> $b } keys %hash);


__DATA__
567         344  
1345        567
2346        78   
3456        67 
3456        789
4678        45    
5349        6
6700        124 
6700        50
8964        560