#include <bits/stdc++.h>
int main(void) {
  unsigned long int h, w, ans;
  scanf("%ld%ld", &h, &w);
  if (h <= 1000000000 && h >= 1) {
    if (w <= 1000000000 && w >= 1) {
      if ((h * w) % 2 == 1) {
        printf("%ld", (h * w) / 2 + 1);
      } else if ((h * w) % 2 == 0) {
        printf("%ld", (h * w) / 2);
      }
    }
  }
  return 0;
}
