#include <iostream>
#include <algorithm>
using namespace std;
 
int main(void){
  int A, B;
  cin >> A >> B;
  int count = 0;
  for(int i = A; i <= B; i++){
      if(0 == (A + B + i) % 3){
          count++;
          
      }
      
  }
  cout << count << endl;
  return 0;
}