#include <iostream>

using namespace std;
int main(){
    long long n,m; cin >> n >> m;
    if(n%2==0 && m%2==0){
        cout << 0 << endl;
        return 0;
    }
    if(m%2==0 && n%2==1) swap(n,m);
    if(n%2==0){
        if(m%2==1){
            cout << n/4 << endl;
            return 0;
        }
    }
    if(n==1){
        cout << m/4 << endl;
        return 0;
    }
    if(m==1){
        cout << n/4 << endl;
        return 0;
    }
    if(n==3){
        cout << m/4 << endl;
        return 0;
    }
    if(m==3){
        cout << n/4 << endl;
        return 0;
    }
    if(n%4==1 && m%4==1){
        cout << n/4 + m/4 << endl;
        return 0;
    }
    if(n%4==1 && m%4==3){
        cout << n/4 + m/4 << endl;
        return 0;
    }
    if(n%4==3 && m%4==1){
        cout << n/4 + m/4 << endl;
        return 0;
    }
    if(n%4==3 && m%4==3){
        cout << (n/4 - 1) + (m/4 - 1) + 4 << endl;
        return 0;
    }
}