#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
int 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;
}