import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {
    static int nombre = 0;

    public static void main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        Scanner in = new Scanner(System.in);
		long n = in.nextInt(); 
        long m = in.nextInt(); 
        long nombre = (n*m)-1;
        
        
        System.out.println(nombre);
        
        
    
    }
    public static int couperEn2 (long n, long m){
        if(( n > m && m != 1) || (n == 1 && m != 1 )){
            nombre++;
            if(( m % 2 == 1)){
                couperEn2 (n, m/2);
                couperEn2 (n, m/2 + 1);
            }else{
                couperEn2 (n, m/2);
                couperEn2 (n, m/2);
            }
        } else if ((n <= m && n != 1) || (m == 1 && n != 1)){
            nombre++;
            if( n % 2 == 1){
                couperEn2 (n/2, m);
                couperEn2 (n/2 + 1, m);
            } else{
                couperEn2 (n/2, m);
                couperEn2 (n/2, m);
            }
           
        }
        return nombre;
    }
}