#include <bits/stdc++.h>
using namespace std;
const int INF = 1 << 29;
const double EPS = 1e-9;
const int dx[] = {1, 0, -1, 0}, dy[] = {0, -1, 0, 1};
int n, m;
int main() {
  cin >> n >> m;
  int ans = 0;
  for (int i = 0; i <= n; i++) {
    int tmp = 0;
    int a1 = i;
    int b1 = (m - 2 * i);
    if (b1 < 0) break;
    int r1, r2;
    r1 = n - i;
    r2 = (m - 2 * i);
    int a2 = (r1 / 2);
    int b2 = r2 - a2;
    if (b2 < 0) {
      tmp = i + r2;
    } else {
      tmp = i + a2;
    }
    ans = max(ans, tmp);
  }
  cout << ans << endl;
  return 0;
}
