/in/foo.cc: In function 'void dfs(int, char, char, char)':
/in/foo.cc:4:6: warning: infinite recursion detected [-Winfinite-recursion]
    4 | void dfs(int n,char a,char b,char c)
      |      ^~~
/in/foo.cc:8:12: note: recursive call
    8 |         dfs(n-1,a,c,b);
      |         ~~~^~~~~~~~~~~