#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  if (n > m) swap(n, m);
  if (n == 1)
    cout << m;
  else if (n == 2)
    cout << ((m / 4) * 4) + ((min(2, m % 4)) * 2);
  else
    cout << ((m + 1) / 2) * ((n + 1) / 2) + (n / 2) * (m / 2);
  return 0;
}
