题解 | 被3整除

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        String[] inputS = new Scanner(System.in).nextLine().trim().split(" ");
        long l = Long.parseLong(inputS[0]), r = Long.parseLong(inputS[1]);

        long cur = 0, times=0, num=1;
        while(times<l) {
            cur+=num;
            times+=1;
            num+=1;
        }

        long res = 0;
        while(times<=r){
            if(cur%3==0) res+=1;
            cur+=num;
            times+=1;
            num+=1;
        }

        System.out.println(res);
    }
}

记得要用long，不然会超出范围