#include<stdio.h>
#include<iostream>
#include<string>
#include<vector>
#include<stack>
using namespace std;
int main() {  
    int l, r;
    while (cin >> l >> r) {
        int res = 0;
        for (int i = l; i <= r; i++) {
            if (i%3==2||i%3==0) {
                res++;
            }
        }
        cout << res << endl;
        return 0;
    }