#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    int a, b;
    cin >> a >> b;

    int k = 0;
    for (int i = a; i <= b; i++) {
        if ((a + b + i) == (a + b + i) / 3 * 3) k++;
    }

    cout << k << endl;

    return 0;
}