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