foo.c: In function 'main':
foo.c:19:10: warning: unused variable 'flg' [-Wunused-variable]
  int n,m,flg;
          ^~~
foo.c:20:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n); 
  ^~~~~~~~~~~~~~
foo.c:21:22: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  for(int i=0;i<n;++i)scanf("%d",a+i);
                      ^~~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务