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 ans = 0;
    for(int i = a; i <= b; i++) {
      if((a + b + i) % 3 == 0) ans++;
    }
    System.out.println(ans);
  }
}