import java.io.*;
import java.util.*;

public class Solution {


    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

		Long cuts = 0L;
        Long n = sc.nextLong();
        Long m = sc.nextLong();
        List<Pair> list = new ArrayList<>();
        list.add(new Pair(n, m));

        while(!list.isEmpty()){
        	List<Pair> res = cut(list.get(0));
        	if(res != null){
                list.addAll(res);
                cuts++;
            }
	        list.remove(0);
        }

        System.out.println(cuts);
    }

    public static boolean canCut(Pair p){
    	return (p.n > 1 || p.m > 1);
    }

    public static List<Pair> cut(Pair p){
    	List<Pair> result = null;
    	if(canCut(p)){
    		result = new ArrayList<>(2);
    		if(p.n > 1){
    			result.add(new Pair(1L, p.m));
    			result.add(new Pair(p.n - 1L, p.m));
    		}else if(p.m > 1){
    			result.add(new Pair(p.n, 1L));
    			result.add(new Pair(p.n, p.m - 1L));
    		}
    		return result;
    	}
    	return result;
    }
}

class Pair{
	Long n;
	Long m;
	public Pair(Long n, Long m){
		this.n = n;
		this.m = m;
	}
}