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 Kotlin (judge verdict: Runtime Error)


fun main(args:Array<String>):Unit {
    val (n, q) = readLine()!!.split(' ').map(String::toInt)
    val stacks = Array(n){Stack<Int>()}
    repeat(q){
        val query = readLine()!!.split(' ').map(String::toInt)
        when(query.first()){
            0 -> stacks[query[1]].push(query.last())
            1 -> if (stacks[query.last()].isNotEmpty) println(stacks[query.last()].top())
            else -> stacks[query.last()].pop()
        }
    }
}

sealed class ImmutableList<out T>{
    object Nil:ImmutableList<Nothing>()
    data class Cons<out T>(val head:T, val tail:ImmutableList<T>):ImmutableList<T>()
}
class Stack<T>{
    private var mStack:ImmutableList<T> = ImmutableList.Nil
    fun push(value:T):Unit {
        mStack = ImmutableList.Cons(value, mStack)
    }
    fun top():T = (mStack as ImmutableList.Cons).head
    fun pop():Unit {
        mStack = (mStack as ImmutableList.Cons).tail
    }
    val isEmpty:Boolean
        get() = mStack == ImmutableList.Nil
    val isNotEmpty:Boolean
        get() = !isEmpty
}