#!/bin/python3

import sys

n,m = input().strip().split(' ')
n,m = [int(n),int(m)]
j=0
k=0
if(n%2!=0 or n%2==0 and n>0):
    j=n-1
if(m%2!=0 or m%2==0 and m>0):
    k=m-1

print(m*n-1)