Thread: different between const int*** and int** const

i've continues test come around multi-level pointers, and got trouble too:

Code:

int main() {
  const int*** x;
  x = new const int**;
  *x = new const int*;
  **x = new int;
  // const pointer
  int*** const y = new int**;
  *y = new int*;
  **y = new int;
  return 0;
}

my question is why and where i need use const in allocation a pointer to constant, and why i don't need const in allocation of a constant pointer?

thanks for reply.