#include <bits/stdc++.h>
using namespace std;
int main() {
  long long h, w, a = 0;
  cin >> h >> w;
  if (h % 2 == 0) {
    h = (h / 2) * w;
    a = h;
  } else {
    h = h / 2 + 1;
    for (int i = 0; i < (w); ++i) {
      if (i % 2 == 0) {
        a += h;
      } else {
        a += (h - 1);
      }
    }
  }
  cout << a << endl;
  return 0;
}
