#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <optional>
#include <queue>
#include <set>
#include <sstream>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

int main() {
    int32_t a, b;
    cin >> a >> b;
    int32_t ans = 0;
    for (auto i = a; i <= b; ++i) {
        if ((a + b + i) % 3 == 0)
            ++ans;
    }
    cout << ans << endl;
    return 0;
}