#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <bitset>
#include <cmath>
#include <string>
#define FI first
#define SE second
#define PF push_front
#define PB push_back
#define PPF pop_front
#define PPB pop_back
#define MA make_pair
#define ll long long
#define PA pair<int,int>
#define VE vector<int>
#define VP vector<PA>
#define FOR(i,a,b) for(int i=a;i<b;i++)
#define ROF(i,a,b) for(int i=b-1;i>=a;i--)
#define YES(i) cout<<(i?"YES":"NO")<<endl
#define Yes(i) cout<<(i?"Yes":"No")<<endl
using namespace std;
//
const int INF=1e9+7;
const int mod=1e9+7;
//
//
struct poi{
  int X;int Y;int Z;
  bool operator<(const poi&R)const{
    return X==R.X ? Y==R.Y ? Z<R.Z : Y<R.Y : X<R.X;
  }
};
//
//
int main(){
	int A,B;
	cin>>A>>B;
	int ans=0;
	FOR(i,A,B+1){
		if((A+B+i)/3*3==A+B+i){
			ans++;
		}
	}
	cout<<ans<<endl;
	return 0;
}