#include <bits/stdc++.h>
using ll = long long int;
using ul = unsigned long long int;
namespace lamlib {
template <class T>
inline T abs(const T &a) {
  return (a > 0) ? a : -a;
}
ul gcd(ul a, ul b) { return (!b) ? a : gcd(b, a % b); }
}  // namespace lamlib
int main(int argc, char *argv[]) {
  ll h, n;
  std::cin >> h >> n;
  ll tmp = h * n;
  if (h == 1 || n == 1)
    std::cout << 1 << std::endl;
  else if (!(tmp % 2))
    std::cout << tmp / 2 << std::endl;
  else
    std::cout << tmp / 2 + 1 << std::endl;
  return 0;
}
