CF747B Mammoth's Genome Decoding

给定长度为 n 且只含有 A、T、C、G和? 的字符串s，其中?可以转换为任何一个字母，问是否存在一个字符串，使得将所有的?替换成字母后，A、T、C、G个数相等。

两行 第一行，一个整数n（4

一行，表示将所有的?替换成字母后使得A、T、C、G个数相等的字符串，若不存在输出“===”（不含引号）。

In the first example you can replace the first question mark with the letter 'A', the second question mark with the letter 'G', the third question mark with the letter 'T', then each nucleotide in the genome would be presented twice. In the second example the genome is already decoded correctly and each nucleotide is exactly once in it. In the third and the fourth examples it is impossible to decode the genom.