import java.util.*;

public class Main{
  static StringBuilder sb = new StringBuilder("");
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int I = A;
    int k =0;
    for (int i = A;i <= B ;i++ ) {
      if ((A+B+I)%3==0) {
        k++;
        I++;
      }else{
        I++;
      }
    }
    System.out.println(k);
  }
}