# include <iostream>
# include <iomanip>
# include <algorithm>
#include <regex>

using namespace std;


int main() {
    int a,b;
    cin >> a >> b;
    int cnt = 0;
    for (int i = a; i <= b; i++) {
        float sum = a + b + i;
        int ave_int = sum / 3;
        float ave_flo = sum / 3;
        if (ave_flo == ave_int) {
            cnt++;
        }
    }
    cout << cnt << endl;

}