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