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

public class Solution {

    public static void main(String[] args) {
       Scanner s =new Scanner(System.in);
        long m=s.nextLong();
        long n=s.nextLong();
        long ans=(long)((m*n)-1);
        System.out.println(Math.max(ans,0));
    }
}