#include <iostream>

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