#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
int INF = 1LL << 30;
int MOD = 1e9+7;
main(){
    int A,B,cnt = 0;
    cin >> A >> B;
    for(int i = A;i <= B;i++){
        if((A + B + i ) % 3 == 0)cnt++;
    }
    cout << cnt << endl;
}