#include <bits/stdc++.h>
const long long int mod = 1e9 + 7;
const long long int INF = 10000000000000;
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  ;
  long long int a = 0, b = 0;
  cin >> a >> b;
  if (a == 1 || b == 1)
    cout << "1";
  else {
    a *= b;
    if (a % 2 == 0)
      cout << a / 2;
    else
      cout << a / 2 + 1;
  }
  return 0;
}
