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

int main() {
  int a, b;
  cin >> a >> b;
  int cnt = 0;
  for (int i = a; i <= b; i++) {
    if ((a + b + i) % 3 == 0) {
      cnt++;
    }
  }
  cout << cnt << endl;
}