#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  if (n > m) swap(n, m);
  if (n == 1) {
    cout << m;
    return 0;
  }
  if (n == 2) {
    int n1 = 2 * (m / 4) + min(2, m % 4);
    cout << 2 * n1;
    return 0;
  }
  int n1 = (m + 1) / 2, n2 = m / 2;
  int res = n1 * ((n + 1) / 2) + n2 * (n / 2);
  cout << res;
  return 0;
}
