#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 1e9;
const int MOD = 1e9 + 7;
const ll LINF = 1e18;
int main() {
  ll H, M;
  ll mx = 0;
  ll mn = 0;
  ll c = 1;
  ll count = 0;
  cin >> H >> M;
  if (H % 2 == 0 || M % 2 == 0) {
    cout << (H * M) / 2 << endl;
  } else if (H == c && M == c) {
    cout << 1 << endl;
  } else if (H % 2 == 1 && M % 2 == 1) {
    count = ((H * M) / 2) + 1;
    cout << count << endl;
  }
}
