#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>

int main() {
    long int a,b;
    scanf("%ld %ld",&a,&b);
    if((a%2==0 && b%2==0)||(a%2!=0 && b%2!=0))
       printf("%ld",((a*b)-1));
    else if((a%2==0 && b%2!=0)||(a%2!=0 && b%2==0))
      printf("%ld",(a*b)-1);
       
    return 0;
}