/in/foo.c:4:11: error: unknown type name 'subject'
 int Solve(subject s, int n, int r, int x);
           ^~~~~~~
/in/foo.c: In function 'main':
/in/foo.c:10:5: error: unknown type name 'subject'
     subject s = politics;
     ^~~~~~~
/in/foo.c:10:5: note: use 'enum' keyword to refer to the type
/in/foo.c:11:18: warning: implicit declaration of function 'Solve' [-Wimplicit-function-declaration]
     int result = Solve(s, n, 1, x);
                  ^~~~~
/in/foo.c: At top level:
/in/foo.c:16:11: error: unknown type name 'subject'
 int Solve(subject s, int n, int r, int x)
           ^~~~~~~