#include <bits/stdc++.h>
using namespace std;
int main() {
  long long p, q;
  cin >> p;
  cin >> q;
  int count = 0;
  for (long long i = 0; i < p; i++) {
    for (long long j = 0; j < q; j++) {
      if ((i + j) % 2 == 0) {
        count++;
      }
    }
  }
  cout << count << endl;
}
