/in/foo.c: In function 'main':
/in/foo.c:7:4: warning: implicit declaration of function 'CS' [-Wimplicit-function-declaration]
  k=CS(n);
    ^~
/in/foo.c: In function 'CS':
/in/foo.c:14:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^