import sys
import math
def i():return int(sys.stdin.readline().replace("\n",""))
def i2():return map(int,sys.stdin.readline().replace("\n","").split())
def s():return str(sys.stdin.readline().replace("\n",""))
def l():return list(sys.stdin.readline().replace("\n",""))
def intl():return [int(k) for k in sys.stdin.readline().replace("\n","").split()]
def lx():return list(map(lambda x:int(x)*-1,sys.stdin.readline().replace("\n","").split()))
def t():return tuple(map(int,sys.stdin.readline().replace("\n","").split()))

if __name__ == "__main__":pass
h,w = i2()
print(h*w//2 if h*w%2 == 0 else h*w//2+1)