# include <iostream>
# include <algorithm>
# include <vector>
# include <string>
# include <set>
# include <map>
# include <cmath>
# include <iomanip>
# include <functional>
# include <utility>
# include <stack>
# include <queue>
# include <list>
# include <bitset>
# include <complex>
#include<limits.h>
#include<unordered_map>
#include<unordered_set>
#include<deque>
#include<cstdio>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const int N = 1000000;
const int mod = 1000000007;
const int INF = 1 << 30;
#define rep(i,n) for(ll i=(ll)0;i<(ll)n;++i)
#define ALL(x) x.begin(),x.end()
#define pp pair<ll,ll>
#define fi first
#define se second
#define pb push_back
#define fix(n) fixed<<setprecision(n)
#define itr vector<ll>::iterator
int dx[4] = { 0,1,0,-1 }, dy[4] = { 1,0,-1,0 };
string YN(bool b) { return(b ? "YES" : "NO"); }
string yn(bool b) { return(b ? "Yes" : "No"); }
ll a, b, c=0;
int main() {
	cin >> a >> b;
	for (int i = a; i <= b;++i)if ((a + b + i) % 3 == 0)++c;
	cout << c << endl;
	return 0;
}