/in/foo.c:4:7: error: expected ')' before 'b'
 LL(LL b)
       ^
/in/foo.c: In function 'main':
/in/foo.c:17:20: error: 'n' undeclared (first use in this function)
     scanf("%lld", &n);
                    ^
/in/foo.c:17:20: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:18:5: warning: implicit declaration of function 'pow_mod' [-Wimplicit-function-declaration]
     printf("%lld", pow_mod(2, n, MOD));
     ^
/in/foo.c:18:34: error: 'MOD' undeclared (first use in this function)
     printf("%lld", pow_mod(2, n, MOD));
                                  ^