/**********************************************************************************/
/*  Problem: d490 "我也愛偶數" from 板橋高中                             */
/*  Language: JAVA (477 Bytes)                                                    */
/*  Result: AC(90ms, 2.4MB) judge by this@ZeroJudge                               */
/*  Author: ssc24 at 2011-09-26 12:32:12                                          */
/**********************************************************************************/


package javaapplication42;
import java.util.*;
import java.math.*;



public class JavaApplication42 {


  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);

    while (sc.hasNext()){
      int a = sc.nextInt();
      int b = sc.nextInt();
      int sum=0;
      for(int i=a;i<=b;i++){
        if(i%2==0){
          sum += i;
        }
      }
      System.out.println(sum);
    }//whlle*/
  }//main

}//class