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 Go (1.6) (judge verdict: Wrong Answer)

package main

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

type City struct {
	n int
	p int
	y int
}

type Citys []City

func (l Citys) Len() int {
	return len(l)
}

func (l Citys) Less(i, j int) bool {
	if l[i].p == l[j].p {
		return l[i].y < l[j].y
	}
	return l[i].p < l[j].p
}

func (l Citys) Swap(i, j int) {
	l[i], l[j] = l[j], l[i]
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Scan()
	sc.Text()
	sc.Scan()
	m, _ := strconv.Atoi(sc.Text())

	citys := make(Citys, m)
	for i := 0; i < m; i++ {
		sc.Scan()
		p, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		y, _ := strconv.Atoi(sc.Text())
		citys[i] = City{i, p, y}
	}

	sort.Sort(citys)
	ans := make([]string, m)
	last := citys[0].p
	n := 0
	for _, c := range citys {
		if c.p == last {
			n++
		} else {
			n = 1
		}
		ans[c.n] = fmt.Sprintf("%06d%06d", c.p, n)
	}

	for _, a := range ans {
		fmt.Println(a)
	}
}