#include <bits/stdc++.h>
int main(void) {
  unsigned long long a, b, c;
  scanf("%llu %llu", &a, &b);
  c = a * (b / 2);
  if (b % 2 == 1) {
    if (a % 2 == 0) {
      c = c + (a / 2);
    } else {
      c = c + (a / 2) + 1;
    }
  }
  if (a == 1 || b == 1) c = 1;
  printf("%llu\n", c);
  return 0;
}
