#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<cmath>
#include<stdio.h>
#include<queue>
#include <climits>
#include <map>
#include <set>
const int mod = 1e9 + 7;
const long long INF = 1LL << 60;
using namespace std;
typedef long long ll;

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