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