#include <bits/stdc++.h>
int main() {
  int n, m;
  while (~scanf("%d%d", &n, &m)) {
    if (n == 1)
      printf("%d\n", m);
    else if (m == 1)
      printf("%d\n", n);
    else if (m == 2) {
      if ((n / 2) % 2 == 0)
        printf("%d\n", 4 * ((n / 2) - n / 4) + (n % 4) * 2);
      else {
        printf("%d\n", 4 * ((n / 2) - n / 4));
      }
    } else if (n == 2) {
      if ((m / 2) % 2 == 0)
        printf("%d\n", 4 * ((m / 2) - m / 4) + (m % 4) * 2);
      else {
        printf("%d\n", 4 * ((m / 2) - m / 4));
      }
    } else {
      if (m % 2 == 0 && n % 2 == 0)
        printf("%d\n", (n / 2) * m);
      else {
        if (m % 2 != 0 && n % 2 != 0)
          printf("%d\n", (m / 2) * (n / 2) + ((m + 1) / 2) * ((n + 1) / 2));
        else if (n % 2 != 0 && m % 2 == 0)
          printf("%d\n", (m / 2) * ((n + 1) / 2) + (m / 2) * (n / 2));
        else {
          printf("%d\n", (n / 2) * ((m + 1) / 2) + (m / 2) * (n / 2));
        }
      }
    }
  }
  return 0;
}
