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

public class Solution {

    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);
        int n = in.nextInt();
        int m = in.nextInt();
        int cuts = cut(n, m);
        System.out.printf("%d", cuts);
    }
    
    public static int cut(int n, int m) {
        if (n == 1 && m == 1) {
            return 0;
        }
        else if (n == 1 && m > 1) {
            return 1 + cut(1, m - 1);
        }
        else if (n > 1 && m == 1) {
            return 1 + cut(n - 1, 1);
        }
        else if (n > m) {
            return 1 + cut(n, 1) + cut(n, m - 1);
        }
        else {
            return 1 + cut(1, m) + cut(n - 1, m);
        }
    }
}