#include <bits/stdc++.h>
using namespace std;
int main(){
  long long N, M;
  cin >> N >> M;
  if (N % 2 == 0 && M % 2 == 0){
    cout << 0 << endl;
  } else if (!(N % 2 == 1 && M % 2 == 1)){
    if (N % 2 == 1){
      swap(N, M);
    }
    cout << M / 4 << endl;
    //N even M odd
    
    //abababa
    //cdcdcdc
    //abababa
    //cdcdcdc
  } else {
    assert(false);
  }
}