#include <bits/stdc++.h>
using namespace std;
#define modulo 1000000007
#define mod(mod_x) ((((long long)mod_x+modulo))%modulo)
#define Inf 2000000000000000000

int main(){
	
	long long N,M;
	cin>>N>>M;
	
	long long ans = 0LL;
	
	if(N%2==1){
		ans += M/4;
	}
	if(M%2==1){
		ans += N/4;
	}
	
	cout<<ans-1<<endl;
	
	return 0;
}