Problem:
Score: 300 points

Problem Statement

In Republic of Atcoder, there are N prefectures, and a total of M cities that belong to those prefectures.

City i is established in year Y_i and belongs to Prefecture P_i.

You can assume that there are no multiple cities that are established in the same year.

It is decided to allocate a 12-digit ID number to each city.

If City i is the x-th established city among the cities that belong to Prefecture i, the first six digits of the ID number of City i is P_i, and the last six digits of the ID number is x.

Here, if P_i or x (or both) has less than six digits, zeros are added to the left until it has six digits.

Find the ID numbers for all the cities.

Note that there can be a prefecture with no cities.

Constraints

1 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq P_i \leq N

1 \leq Y_i \leq 10^9

Y_i are all different.

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N M
P_1 Y_1
:
P_M Y_M

Output

Print the ID numbers for all the cities, in ascending order of indices (City 1, City 2, ...).

Sample Input 1

2 3
1 32
2 63
1 12

Sample Output 1

000001000002
000002000001
000001000001

As City 1 is the second established city among the cities that belong to Prefecture 1, its ID number is 000001000002.

As City 2 is the first established city among the cities that belong to Prefecture 2, its ID number is 000002000001.

As City 3 is the first established city among the cities that belong to Prefecture 1, its ID number is 000001000001.

Sample Input 2

2 3
2 55
2 77
2 99

Sample Output 2

000002000001
000002000002
000002000003

Solution in C (GCC 5.4.1) (judge verdict: Wrong Answer)

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

void mergesort(int y[], int p[], int a[], int i, int j);
void merge(int y[], int p[], int a[], int i, int j);

int main(void)
{
	int n, m, k, *y, *p, *a, *no;
	scanf("%d%d", &n, &m);
	p=(int *)malloc(sizeof(int)*m);
	y=(int *)malloc(sizeof(int)*m);
	a=(int *)malloc(sizeof(int)*m);
	no=(int *)malloc(sizeof(int)*m);

	for (int i = 0; i < m; ++i)
	{
		scanf("%d%d", &p[i], &y[i]);
	}

	for (int i = 0; i < m; ++i)
	{
		a[i] = i;
	}

	mergesort(y, p, a, 0, m-1);

	for (int i = 1; i <= n; ++i)
	{
		k = 1;
		for (int j = 0; j < m; ++j)
		{
			if (p[j] == i)
			{
				no[a[j]] = i*1000000+k;
				k++;
			}
		}
	}

	for (int i = 0; i < m; ++i)
	{
		printf("%012d\n", no[i]);
	}

	return 0;
}

void mergesort(int y[], int p[], int a[], int i, int j)
{
	if (i-j == 0)
	{
		return;
	}
	else
	{
		mergesort(y, p, a, i, (i+j)/2);
		mergesort(y, p, a, (i+j)/2+1, j);
		merge(y, p, a, i, j);
		return;
	}
}

void merge(int y[], int p[], int a[], int i, int j)
{
	int l, r;
	int y2[j];
	int p2[j];
	int a2[j];
	l=i;
	r=(i+j)/2+1;
	for (int k = i; k <= j; ++k)
	{
		if (l > (i+j)/2)
		{
			y2[k] = y[r];
			p2[k] = p[r];
			a2[k] = a[r];
			r++;
		} else if (r > j)
		{
			y2[k] = y[l];
			p2[k] = p[l];
			a2[k] = a[l];
			l++;
		} else if (y[l] <= y[r])
		{
			y2[k] = y[l];
			p2[k] = p[l];
			a2[k] = a[l];
			l++;
		} else
		{
			y2[k] = y[r];
			p2[k] = p[r];
			a2[k] = a[r];
			r++;
		}
	}
	for (int k = i; k <= j; ++k)
	{
		y[k]=y2[k];
		p[k]=p2[k];
		a[k]=a2[k];
	}
	return;
}