foo.cc: In function 'bool init()':
foo.cc:21:39: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   21 |           for (int i=1;i<=n;i++) scanf("%d", &a[i]);
      |                                  ~~~~~^~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务