def scanf(scanstr,data_format):
    scanstr=scanstr.split(" ")
    if(type(data_format) is not list):
        print("data_format error")
    if(len(scanstr)!=len(data_format)):
        print("Error")
        return -1
    j=0
    for kata in data_format:
        if(kata=="str"):
            scanstr[j]=str(scanstr[j])
        if(kata=="int"):
            scanstr[j]=int(scanstr[j])
        j=j+1
    return scanstr
data=mylib.scanf(input(),["int","int"])
if data[0]!=1 and data[1]!=1:
    print(str(round(float(data[0]*data[1])/2.0+0.1)))
else:
    print(1)