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