#include <bits/stdc++.h>
using namespace std;
int main(){
  long long N, M;
  cin >> N >> M;
  long long a = ((N + 1) / 2) * ((M + 1) / 2);
  long long b = ((N + 1) / 2) * (M / 2);
  long long c = (N / 2) * ((M + 1) / 2);
  long long d = (N / 2) * (M / 2);
  long long m = min({a, b, c, d});
  a -= m;
  b -= m;
  c -= m;
  d -= m;
  long long ans = (a + b + c + d) / 4;
  if (abs(a + d - b - c) <= 1){
    ans--;
  }
  cout << ans << endl;
}