#include <bits/stdc++.h>
using namespace std;
int main() {
  unsigned long h, w;
  cin >> h >> w;
  unsigned long ans;
  if (h % 2 == 0) {
    ans = int(h / 2) * w;
  } else {
    if (w % 2 == 0) {
      int a = (h / 2) + 1;
      int b = (h / 2);
      ans = (a + b) * w / 2;
    } else {
      int a = (h / 2) + 1;
      int b = (w / 2) + 1;
      ans = a * b + (h / 2) * (w / 2);
    }
  }
  cout << ans << "\n";
  return 0;
}
