import java.util.*;


public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int answer=0;
    for(int i=a;i<=b;i++){
      if((a+b+i)%3==0){
        answer++;
      }
    }
    System.out.println(answer);
  }
}