($a,$b)=glob<>;
($a,$b)=($b,$a)if$a<$b;
if($a%2==0){
	if($b%2==0){
		$r=$a*$b+$b+1;
	}
	if($b%2==1){
		$r=($a*2-2)*($b+0)/2+4;
	}
}
if($a%2==1){
	if($b%2==0){
		$r=($a*2+1)*$b/2+1;
	}
	if($b%2==1){
		$r=($a*2+1)*($b+1)/2-1;
	}
}
if($a==2&$b==2){
	$r=$a*2+2;
}
if($b==0){
	$r=1;
}
if($a==0){
	$r=0;
}
print$r;