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