#include <bits/stdc++.h>
using namespace std;
#define int long long

signed main() {
  int A, B;
  cin >> A >> B;

  int ans = 0;
  for (int i = A; i <= B; i++) {
    if ((A + B + i) % 3 == 0) ans++;
  }

  cout << ans << endl;
  return 0;
}