#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n, m, ans1 = 0, ans2 = 0, ans3 = 0, ans4 = 0;
  cin >> n >> m;
  if (n > m) {
    swap(n, m);
  }
  if (n == 1) {
    return cout << m, 0;
  }
  if (n == 2) {
    if (m % 4 == 3) {
      return cout << m + 1, 0;
    } else {
      return cout << m + m % 4, 0;
    }
  }
  for (int i = 1; i <= n; i++) {
    if (i & 1) {
      ans1 += (m + 1) / 2;
      ans2 += m / 2;
    } else {
      ans1 += m / 2;
      ans2 += (m + 1) / 2;
    }
  }
  for (int i = 1; i <= m; i++) {
    if (i & 1) {
      ans3 += (n + 1) / 2;
      ans4 += n / 2;
    } else {
      ans3 += n / 2;
      ans4 += (n + 1) / 2;
    }
  }
  cout << max({ans1, ans2, ans3, ans4});
}
