#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <tuple>
#include <cstdint>
#include <cstdio>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <deque>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <cctype>
#include <functional>
#include <ctime>
#include <fstream>
#include <cmath>
#include <limits>
#include <numeric>
#include <type_traits>
#include <iomanip>
#include <float.h>
#include <math.h>
#include <cassert>
#pragma warning (disable: 4996)
using namespace std;
using ll = long long;
int main() {
    ll n, m;
    cin >> n >> m;
    if (n % 2 == 0 && m % 2 == 0)cout << 0 << endl;
    else if (n % 2 == 0)cout << m / 4 << endl;
    else if (m % 2 == 0)cout << n / 4 << endl;
    else if (n % 4 == 1 || m % 4 == 1)cout << n / 4 + m / 4 << endl;
    else if (n == 3)cout << m / 4 << endl;
    else if (m == 3)cout << n / 4 << endl;
    else cout << n / 4 + m / 4 + 2 << endl;
}