#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int H, W;
  cin >> H >> W;
  if (H == 1 || W == 1)
    cout << "1"
         << "\n";
  else if (H % 2 == 0)
    cout << H / 2 * W << "\n";
  else
    cout << H / 2 * W + W - W / 2 << "\n";
}
