#include <bits/stdc++.h>
using namespace std;
int main(void) {
  unsigned long long h, w;
  unsigned long long num;
  cin >> h >> w;
  if (h % 2 == 0) {
    num = w * (unsigned long long)(h / 2);
  } else {
    if (w % 2 == 0) {
      num = w * (unsigned long long)(h / 2) + (unsigned long long)(w / 2);
    } else {
      num = w * (unsigned long long)(h / 2) + (unsigned long long)(w / 2) + 1;
    }
  }
  cout << num << endl;
  return 0;
}
