#!/usr/bin/perl -w
use strict;
require Math::BigPositiveOkayPrecision;

print countPairPermutations( @ARGV ), $/;

sub countPairPermutations
{
    my( $x, $y )= @_;
    ( $x, $y )= ( $y, $x )
        if  $y < $x;
    my $p= Math::BigPositiveOkayPrecision->new( 1 );
    for my $i (  1 .. $x  ) {
        $p= $p * ( $y+$i ) / $i;
    }
    return $p;
}