#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; ++i)
typedef long long ll;
using namespace std;

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;

    return 0;
}