#include <cstdio>
using namespace std;

int main() {
  int h, w;
  scanf("%d%d",&h, &w);
  int p = h * w;
  h == 1 || w == 1 ? printf(1) ? p % 2 == 0 ? printf("%d", p / 2) : printf("%d", p / 2 + 1);
  return 0; 
}