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