($n,$pa,$pb)=<>=~/\S+/g;
@a=sort{$a<=>$b}<>=~//g;
@b=sort{$a<=>$b}<>=~//g;

sub f{
    my@a=@{$_[0]};
    my@b=@{$_[1]};
    my$c=$_[2];
    my$m="@a,@b,$c";
    my$p=$$m;
    if(!defined $p){
	if(@a==1){
	    $p=$c+($a[0]+$b[0])*($a[0]>$b[0]?1:-1)>0;
	}else{
	    my $qa=(1-$pa)/(@a-1);
	    my $qb=(1-$pb)/(@b-1);
	    for my$i(0..@a-1){
		for my$j(0..@b-1){
		    $p+=($i?$qa:$pa)*($j?$qb:$pb)*f([@a[0..$i-1,$i+1..@a-1]],[@b[0..$j-1,$j+1..@b-1]],$c+($a[$i]+$b[$j])*($a[$i]>$b[$j]?1:-1));
		}
	    }
	}
	$$m=$p+0;
    }
    $p;
}

print f(\@a,\@b,0);