#include <bits/stdc++.h>
using namespace std;
int main() {
  vector<int> vec;
  long int num1 = 0;
  long int num2 = 0;
  cin >> num1 >> num2;
  if (num1 == 1 || num2 == 1) {
    cout << 1 << endl;
  } else if (num1 * num2 % 2 == 0) {
    cout << num1 * num2 / 2 << endl;
  } else {
    cout << num1 * num2 / 2 + 1 << endl;
  }
}
