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