#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long h, w;
  cin >> h >> w;
  if (h == 1 || w == 1) {
    cout << 1 << "\n";
  } else {
    cout << (h * w + 1) / 2 << "\n";
  }
  return 0;
}
