H, W = map(int, input().split())
result=0
if H==1 or W==1:
    result=1
elif W%2==0:
    result = (W/2)*H
else:
    if H%2==0:
        result=W*(H/2)
    else :
        result=W*(H-1)/2+(W+1)/2
print(str(round(result)))
