#include <bits/stdc++.h>
#define rep(i,a,b) for(int i=a;i<(b);++i)
#define erep(i,a,b) for(int i=a;i<=(int)(b);++i)
#define per(i,a,b) for(int i=(a);i>(b);--i)
#define eper(i,a,b) for(int i=(a);i>=b;--i)
#define pb push_back
#define mp make_pair
#define INF 100100100100
#define inf 2001001001
#define MOD 1000000007
#define ALL(x) begin(x),end(x)
#define F first
#define S second
using namespace std;
using ll = long long;
using pii = pair<int,int>;
using vii = vector<int>;
using vll = vector<ll>;
using priority_queue_small = priority_queue<int, vector<int>, greater<int> >;
template<class T>using vv = vector<T>;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a = b; return 1; } return 0; }
template<class T>void show(const vector<T> &a) { for (int i = 0; i < (int)a.size(); ++i) cout << a[i] << (i != (int)a.size()-1 ? " " : "\n"); }
template<class T>T gcd(T a, T b){ return b ? gcd(b, a % b) : a; }
template<class T>T lcm(T a, T b){ return a / gcd(a, b) * b; }
int dy[]={0, 1, -1, 0};
int dx[]={1, 0, 0, -1};
ll n, m;
int main() {
cin.tie(0);
ios::sync_with_stdio(false);
cin >> n >> m;
if (2 * n >= m) cout << m / 2 << endl;
else {
ll ans = n;
m -= 2 * n;
ans += m / 4;
cout << ans << endl;
}
return 0;
}