#include<iostream>
using namespace std;
int main() {
  ll h,w;
  ll ans;
  cin >> h;
  cin >> w;
  
  ans = h * w / 2;
  if(h == 1 && w == 1) {
    ans = 1;
  }else if(w % 2 == 1 && h % 2 == 1) {
    ans++;
  }
  cout << ans << endl;
  return 0;
}