Problem:
Stack

Stack is a container of elements that are inserted and deleted according to LIFO (Last In First Out).

For $n$ stack $S_i$ ($i = 0, 1, ..., n-1$), perform a sequence of the following operations.

push($t$, $x$): Insert an integer $x$ to $S_t$.

top($t$): Report the value which should be deleted next from $S_t$. If $S_t$ is empty, do nothing.

pop($t$): Delete an element from $S_t$. If $S_t$ is empty, do nothing.

In the initial state, all stacks are empty.

Input

The input is given in the following format.

$n \; q$
$query_1$
$query_2$
:
$query_q$

Each query $query_i$ is given by

0 $t$ $x$

or

1 $t$

or

2 $t$

where the first digits 0, 1 and 2 represent push, top and pop operations respectively.

Output

For each top operation, print an integer in a line.

Constraints

$1 \leq n \leq 1,000$

$1 \leq q \leq 200,000$

$-1,000,000,000 \leq x \leq 1,000,000,000$

Sample Input 1

3 9
0 0 1
0 0 2
0 0 3
0 2 4
0 2 5
1 0
1 2
2 0
1 0

Sample Output 1

3
5
2

Solution in Go (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

// Element for Deque
type Element struct {
	value int
}

// Stack based on array
type Stack struct {
	array []Element
}

// NewStack is constructer of Stack
func NewStack() *Stack {
	s := new(Stack)
	return s
}

func (s *Stack) push(x int) {
	element := Element{value: x}
	s.array = append(s.array, element)
}

func (s *Stack) top() (bool, int) {
	if len(s.array) == 0 {
		return false, -1
	}

	top := s.array[len(s.array)-1]
	return true, top.value
}

func (s *Stack) pop() (bool, int) {
	if len(s.array) == 0 {
		return false, -1
	}

	l := len(s.array) - 1
	top := s.array[l]
	s.array = s.array[:l]
	return true, top.value
}

func main() {
	scanner.Split(bufio.ScanWords)
	nStacks := nextInt()
	nQueries := nextInt()

	stacks := make([]Stack, nStacks)

	for i := 0; i < nQueries; i++ {
		queryType := nextInt()
		iStack := nextInt()

		if queryType == 0 {
			x := nextInt()
			stacks[iStack].push(x)
		} else if queryType == 1 {
			ok, value := stacks[iStack].top()
			if ok {
				fmt.Println(value)
			}
		} else {
			stacks[iStack].pop()
		}
	}
}