New Year's Number

Polycarp remembered the $2020$-th year, and he is happy with the arrival of the new $2021$-th year. To remember such a wonderful moment, Polycarp wants to represent the number $n$ as the sum of a certain number of $2020$ and a certain number of $2021$.

Odd Divisor

You are given an integer $n$. Check if $n$ has an odd divisor, greater than one (does there exist such a number $x$ ($x>1$) that $n$ is divisible by $x$ and $x$ is odd).

拯救007

在老电影“007之生死关头”(Live and Let Die)中有一个情节，007被毒贩抓到一个鳄鱼池中心的小岛上，他用了一种极为大胆的方法逃脱 —— 直接踩着池子里一系列鳄鱼的大脑袋跳上岸去！(据说当年替身演员被最后一条鳄鱼咬住了脚，幸好穿的是特别加厚的靴子才逃过一劫。)

Wizard of Orz

There are $n$ digital panels placed in a straight line. Each panel can show any digit from $0$ to $9$. Initially, all panels show $0$.

扫描集

扫描集为一个字符集合，用来匹配期待输入的字符。对于scanf匹配输入内容时，可以使用扫描集灵活地进行字符串截取输入。

扫描集以 % 开头，用 [] 包含字符集。如扫描集 %[abc], %[a-z], %[^abc], %[^a-z] ，其中 ^ 表示求反集。

在阅读文章前，请先思考下面的代码执行结果是什么：

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#include <stdio.h>
int main(){
  struct{
    int x; int y;
  }s[2] = {{2, 0}, {1, 3}}, *p = s;
  printf("%d, %d", ++p->x, (++p)->x);
  return 0;
}

公孙树落金黄色，未着寒衣手泛凉。

行人男女互拍照，余独坐于石台旁。