#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
using namespace std;

int main()
{
    int a, b, cnt = 0;
    cin >> a >> b;
    for (int i = a; i <= b; i++){
        if (!((a + b + i)%3)) cnt++;
    }
    cout << cnt << endl;
}