/in/foo.c:2:1: error: unknown type name 'using'
    2 | using namespace std;
      | ^~~~~
/in/foo.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
    2 | using namespace std;
      |                 ^~~
/in/foo.c: In function 'main':
/in/foo.c:9:9: error: 'cin' undeclared (first use in this function)
    9 |         cin>>a>>m>>k;
      |         ^~~
/in/foo.c:9:9: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:13:17: error: 'cout' undeclared (first use in this function)
   13 |                 cout<<"fee=0"<<endl;
      |                 ^~~~
/in/foo.c:13:32: error: 'endl' undeclared (first use in this function)
   13 |                 cout<<"fee=0"<<endl;
      |                                ^~~~
/in/foo.c:7:19: warning: unused variable 'fee' [-Wunused-variable]
    7 |         double eq,fee;
      |                   ^~~