We use two stacks: s1 for pushing elements and s2 for popping/peeking. When s2 is empty, we transfer all elements from s1 to s2, which reverses their order and achieves FIFO behavior.

1. push(x): Append to s1.
2. pop():
   • If s2 is empty, pop all elements from s1 and push them to s2.
   • Pop from s2.
3. peek():
   • If s2 is empty, transfer from s1 to s2.
   • Return the top of s2.
4. empty(): Return true if both stacks are empty.

• Time Complexity:
  • Push: O(1)
  • Pop/Peek: Amortized O(1). Each element is moved at most twice.
• Space Complexity: O(N).

class MyQueue:
    def __init__(self):
        self.s1 = []
        self.s2 = []

    def push(self, x: int) -> None:
        self.s1.append(x)

    def _transfer(self):
        if not self.s2:
            while self.s1:
                self.s2.append(self.s1.pop())

    def pop(self) -> int:
        self._transfer()
        return self.s2.pop()

    def peek(self) -> int:
        self._transfer()
        return self.s2[-1]

    def empty(self) -> bool:
        return not self.s1 and not self.s2