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