foo.cc: In function 'int main()':
foo.cc:11:17: warning: unused variable 'k' [-Wunused-variable]
   11 |     int n,m,i,j,k,o;
      |                 ^
foo.cc:12:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   12 |     scanf("%d%d%d",&o,&n,&m);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务