#include <bits/stdc++.h>
using namespace std;
int32_t main(void) {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  long long n, m;
  cin >> n >> m;
  if (n == 1 || m == 1) {
    cout << 1 << endl;
    return 0;
  }
  long long ans = ((n * m) + 1) / 2;
  cout << ans << endl;
}
