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 C (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>

int main()
{
  int i,  n, q, nq, t, x;
  fscanf(stdin, "%d %d", &n, &nq);
  int **stack = (int**)malloc(sizeof(int*)*n);
  int *sp = (int*)malloc(sizeof(int)*n);
  for (i=0; i<n; i++) {
    stack[i] = (int*)malloc(sizeof(int)*nq);
    sp[i]=-1;
  }
  
  for (i=0; i<nq; i++) {
    fscanf(stdin, "%d %d", &q, &t);
    switch (q) {
    case 0:
      fscanf(stdin, "%d", &x);
      stack[t][++sp[t]] = x;
      break;
    case 1:
      if (sp[t]>=0)
	printf("%d\n", stack[t][sp[t]]);
      break;
    case 2:
      if (sp[t]>=0) sp[t]--;
    }
  }
  return 0;
}