#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, b;
  cin >> a >> b;
  int ans = 0;
  while ((a >= 1 && b > 1) || (a > 1 && b >= 1)) {
    if (a < b) {
      ans++;
      a--;
      b -= 2;
    } else {
      ans++;
      a -= 2;
      b--;
    }
  }
  cout << ans << endl;
}
