#include<bits/stdc++.h>
using namespace std;
typedef long long ll;

int main(){
  int a, b, count = 0;
  cin >> a >> b;
  for(int i = a;i <= b;i++){
    if((a + b + i) % 3 == 0) count++;
  }
  cout << count << "\n";
  return 0;
}