# -*- coding: utf-8 -*-
from sys import stdin
from operator import itemgetter

# stdin = open("sample.txt")

h, w = [int(x) for x in stdin.readline().rstrip().split()]

if h == 1 or w == 1:
    print(1)
else:
    if h*w % 2 == 0:
        print(h*w // 2)
    else:
        print((h*w + 1) // 2)