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