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