#include <iostream>
#include <set>
#include <vector>
#include <string>
#include <algorithm>
#include <iterator>

using namespace std;

#define rep(i, n) for(int i = 0; i < n; i++)
#define repi(i, n) for(auto i = (n).begin(); i != (n).end(); i++)
#define in_arr(type, a, n) copy_n(istream_iterator<type>(cin), n, (a).begin());

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