//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#define rep(i, n) for(int i=0; i<n; ++i)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
using namespace std;
using ll = int64_t;
using ld = long double;
using P = pair<int, int>;
using vs = vector<string>;
using vi = vector<int>;
using vvi = vector<vi>;
template<class T> using PQ = priority_queue<T>;
template<class T> using PQG = priority_queue<T, vector<T>, greater<T> >;
const int INF = 0xccccccc;
const ll LINF = 922337203685477580LL;
template<typename T1, typename T2>
inline bool chmax(T1 &a, T2 b) {return a < b && (a = b, true);}
template<typename T1, typename T2>
inline bool chmin(T1 &a, T2 b) {return a > b && (a = b, true);}
template<typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) { return is >> p.first >> p.second;}
template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) { return os << p.first << ' ' << p.second;}



//head

int n, m;
int ans;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> m;
  if(~n&1 and ~m&1) {
    cout << 0 << endl;
  }
  else {
    if(n%4 == 3 and m%4 == 3 and n > 4 and m > 4) {
      ans = n/4+m/4;
      ans <<= 1;
      n -= 6;
      m -= 6;
      cout << ans - (n/4+m/4) << endl;
      return 0;
    }
    if(~n&1) {
      cout << (n>>2) << endl;
    }
    else if(~m&1) {
      cout << (m>>2) << endl;
    }
    else {
      cout << ((n>>2) + (m>>2)) << endl;
    }
  }
}