#include "bits/stdc++.h"
#define rep(i,n)for(int i=0;i<(int)(n);i++)
using namespace std;
#define all(a) a.begin(),a.end()
typedef long long ll;
#define vi vector<ll>
typedef pair<ll,ll>P;
const ll inf=1ll<<61;

signed main(){
	ll h,w;cin>>h>>w;
	if(h%2==0&&w%2==0)cout<<0<<endl;
	else if(h%2==0||w%2==0){
		if(h%2==0)swap(h,w);
		cout<<w/4<<endl;
	}
	else{
		if(h%4==3&&w%4==3){
			if(h>w)swap(h,w);
			if(h==3)cout<<w/4<<endl;
			else cout<<4+(h+w-14)/4<<endl;
		}
		else{
			cout<<(h-1)/4+(w-1)/4<<endl;
		}
	}
}