my %edgeHash;
my %countHash;
my %already_seen;
while(<stdin>){

    # Reading an edge list
    if(/^\s*([0-9]+)\s+([0-9]+)\S*$/){
        my $a = "$1";
        my $b = "$2";

        # Eliminate loops
        next if $already_seen{$b};

        push @{$edgeHash{$a}}, $b;
    }
}