#include <bits/stdc++.h>
using namespace std;
const long long INF = 1000000000000;
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;
    long long ans = INF;
    for (int i = 0; i <= min((long long) 2, a); i++){
      for (int j = 0; j <= min((long long) 2, b); j++){
        for (int k = 0; k <= min((long long) 2, c); k++){
          for (int l = 0; l <= min((long long) 2, d); l++){
            long long a2 = a - i;
            long long b2 = b - j;
            long long c2 = c - k;
            long long d2 = d - l;
            if (!(i == 2 && j == 2) && !(1 == 2 && k == 2) && !(j == 2 && l == 2) && !(k == 2 && l == 2)){
              if (a2 % 2 == 0 && b2 % 2 == 0 && c2 % 2 == 0 && d2 % 2 == 0){
                if ((a2 + b2 + c2 + d2) % 4 == 0){
                  ans = min(ans, (a2 + b2 + c2 + d2) / 4);
                }
              }
            }
          }
        }
      }
    }
    cout << ans << endl;
  }
}