#include <bits/stdc++.h>
using namespace std;
int main() {
  int tc, i, j, k, cs = 1, m, n, ans;
  {
    scanf("%d%d", &m, &n);
    if (n > m) swap(m, n);
    if (n == 1)
      ans = m;
    else if (n == 2) {
      ans = (m / 4) * 4;
      if (m % 4 == 1)
        ans += 2;
      else if (m % 4 == 2)
        ans += 4;
      else if (m % 4 == 3)
        ans += 4;
    } else {
      ans = ((m + 1) / 2) * ((n + 1) / 2);
      ans += (m / 2) * (n / 2);
    }
    printf("%d\n", ans);
  }
  return 0;
}
