#include <bits/stdc++.h>
using namespace std;
int main(){
  long long N, M;
  cin >> N >> M;
  if (N == 3 && M == 3){
    cout << 0 << endl;
  } else {
    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;
    cout << (a + b + c + d) / 4 << endl;
  }
}