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: Accepted)

package main

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

var (
	readString func() string
	stdout     *bufio.Writer
)

func init() {
	readString = newReadString(os.Stdin)
	stdout = bufio.NewWriter(os.Stdout)
}

func newReadString(ior io.Reader) func() string {
	r := bufio.NewScanner(ior)
	r.Buffer(make([]byte, 1024), int(1e+11))
	r.Split(bufio.ScanWords)

	return func() string {
		if !r.Scan() {
			panic("Scan failed")
		}
		return r.Text()
	}
}

func readInt() int {
	return int(readInt64())
}

func readInt64() int64 {
	i, err := strconv.ParseInt(readString(), 0, 64)
	if err != nil {
		panic(err.Error())
	}
	return i
}

func readIntSlice(n int) []int {
	b := make([]int, n)
	for i := 0; i < n; i++ {
		b[i] = readInt()
	}
	return b
}

func readLengthAndSlice() (int, []int) {
	n := readInt()
	return n, readIntSlice(n)
}

func printf(f string, args ...interface{}) (int, error) {
	return fmt.Fprintf(stdout, f, args...)
}

func println(args ...interface{}) (int, error) {
	return fmt.Fprintln(stdout, args...)
}

func eprintln(args ...interface{}) (int, error) {
	return fmt.Fprintln(os.Stderr, args...)
}

func eprintf(f string, args ...interface{}) (int, error) {
	return fmt.Fprintf(os.Stderr, f, args...)
}

// readString() string
// readInt() int
// readIntSlice(n int) []int
// readLengthAndSlice() []int

// -----------------------------------------------------------------------------

func main() {
	defer stdout.Flush()
	n := readInt()
	m := readInt()
	c := make([]city, m)
	for i := range c {
		c[i].id = i
		c[i].p = readInt()
		c[i].y = readInt()
	}

	x := make([]int, n+1)
	for i := range x {
		x[i] = 1
	}

	sort.Sort(sortByYear(c))
	for i := range c {
		p := c[i].p
		c[i].z = x[p]
		x[p]++
	}

	sort.Sort(sortById(c))
	for i := range c {
		printf("%06d%06d\n", c[i].p, c[i].z)
	}

}

// -----------------------------------------------------------------------------

type city struct {
	id, p, y, z int
}

type sortByYear []city

func (s sortByYear) Len() int {
	return len(s)
}

func (s sortByYear) Less(i, j int) bool {
	return s[i].y < s[j].y
}

func (s sortByYear) Swap(i, j int) {
	s[i], s[j] = s[j], s[i]
}

type sortById []city

func (s sortById) Len() int {
	return len(s)
}

func (s sortById) Less(i, j int) bool {
	return s[i].id < s[j].id
}

func (s sortById) Swap(i, j int) {
	s[i], s[j] = s[j], s[i]
}