foo.c:3:1: error: unknown type name 'using'
    3 | using namespace std;
      | ^~~~~
foo.c:3:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
    3 | using namespace std;
      |                 ^~~
foo.c: In function 'main':
foo.c:8:2: error: 'cin' undeclared (first use in this function)
    8 |  cin>>l>>m;
      |  ^~~
foo.c:8:2: note: each undeclared identifier is reported only once for each function it appears in
foo.c:23:2: error: 'cout' undeclared (first use in this function)
   23 |  cout<<j;
      |  ^~~~

[Hydro](https://hydro.ac)提供评测服务