#include <stdio.h>
int main(void){
int H,W,X;
long Y;
scanf("%d  %d",&H,&W);
if(H == 1 || W == 1)
{
printf("1");
}
if (H * W %2 == 0)
{
X= (H * W ) / 2;
printf("%d" ,X);
}
 else
{
Y= (H * W) / 2 + 1;
 printf("%1d" ,Y);
}
return 0;
}