#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <array>
#include <map>
#include <stack>
#include <queue>
#include <set>
#include <cmath>
#include <numeric>

using namespace std;


int main() {

    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int A, B;
    cin >> A >> B;
    int count = 0;
    for (int i = A; i <= B; ++i) {
        if ((A + B + i) % 3 == 0) {
            count += 1;
        }
    }

    cout << count << "\n";
}