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