#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
int main(){
    int a, b;
    cin >> a >> b;
    int r = (a+b)%3;
    a+=r,b+=r;
    cout << (b/3-(a-1)/3) << endl;
    return 0;
}