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