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