#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

int A, B, ans;

int main() {
  cin >> A >> B;
  for (int i = A; i <= B; i++) {
    if ((A + B + i) % 3 == 0) ans++;
  }
  cout << ans << endl;
  return 0;
}