#include<bits/stdc++.h>

#define INF 1000000007
#define LINF 1000000000000000007

using namespace std;

typedef long long Int;
typedef pair<Int, Int> P;

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