codeforces 688B Lovely Palindromes_pari has a friend who loves palindrome numbers. a -优快云博客

本文链接：https://blog.youkuaiyun.com/zhang__liuchen/article/details/76718788

本文介绍了一个程序设计问题，即如何找出指定序号的偶数位正回文数。回文数是一种特殊的整数，无论从前往后还是从后往前读都相同。文章特别关注那些具有偶数位数的回文数，并提供了一个示例程序来解决这个问题。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

Pari has a friend who loves palindrome numbers. A palindrome number is a number that reads the same forward or backward. For example 12321, 100001 and 1 are palindrome numbers, while 112 and 1021 are not.

Pari is trying to love them too, but only very special and gifted people can understand the beauty behind palindrome numbers. Pari loves integers with even length (i.e. the numbers with even number of digits), so she tries to see a lot of big palindrome numbers with even length (like a 2-digit 11 or 6-digit 122221), so maybe she could see something in them.

Now Pari asks you to write a program that gets a huge integer n from the input and tells what is the n-th even-length positive palindrome number?

Input

The only line of the input contains a single integer n (1 ≤ n ≤ 10100 000).

Output

Print the n-th even-length palindrome number.

   Examples
 
     input
   
1

     output
   
11

     input
   
10

     output
   
1001

Note

The first 10 even-length palindrome numbers are 11, 22, 33, ... , 88, 99 and 1001.

就是回文的定义。

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
char s[1000005];
int main()
{
    scanf("%s",s);
    printf("%s",s);
    int n=strlen(s);
    for(int i=n-1;i>=0;i--)
        printf("%c",s[i]);
    printf("\n");
    return 0;
}