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