Sorted Stack

You are tasked with implementing a SortedStack class that stores integers in a stack data structure so that its elements are always sorted in ascending order. The smallest element should be at the top of the stack.

The SortedStack class should support the following operations:

• push(val): Inserts an integer val into the stack while maintaining the sorted order.
• pop(): Removes the element at the top of the stack. If the stack is empty, do nothing.
• peek(): Returns the top element of the stack (i.e. the smallest element) without removing it. Returns -1 if the stack is empty.
• isEmpty(): Returns True if the stack is empty, otherwise returns False.

Note: The stack must always be sorted in ascending order after every operation. In other words, if you perform a series of push and pop operations, the peek operation must always return the smallest element currently in the stack.

Constraints:

• The number of elements in the stack will be in the range \([0, 10^5]\).
• \(-10^6 \leq val \leq 10^6\).
• You will make at most \(10^5\) calls to push, pop, peek, and isEmpty.

Input/Output is handled via standard input and output. The first line of input contains an integer n, the number of operations. Each of the following n lines contains one operation in one of the following forms:

• push x where x is an integer.
• pop
• peek
• isEmpty

For each peek and isEmpty operation, output the result on a new line.

Example:

Input:
10
push 3
push 2
push 4
peek
pop
peek
pop
peek
pop
isEmpty
Output:
2
3
4
True

</p>

inputFormat

The first line of input is an integer n which represents the number of operations. The next n lines describe the operations to be performed on the SortedStack. Each operation is one of the following forms:

• push x (where x is an integer)
• pop
• peek
• isEmpty

outputFormat

For every peek and isEmpty operation, output the result to the standard output on a new line. For a peek operation, output the smallest element in the stack (or -1 if the stack is empty), and for an isEmpty operation, output True if the stack is empty, otherwise False.

## sample

10
push 3
push 2
push 4
peek
pop
peek
pop
peek
pop
isEmpty

2
3
4
True

</p>