描述：给定字符串 num（非负整数）和整数 k，移除 k 位数字，使剩余数字最小。以字符串形式返回（不含前导零）。
Жители Санкт-Петербурга устроили «крысогон»17:52
，更多细节参见下载安装 谷歌浏览器 开启极速安全的 上网之旅。
‘Unbelievably dangerous’: experts sound alarm after ChatGPT Health fails to recognise medical emergencies | Study finds ChatGPT Health did not recommend a hospital visit when medically necessary in more than half of cases
understood by beginners and advanced users alike.