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 provides
//
// File:  c.go
// Author: ymiyamoto
//
// Created on Mon Dec 17 17:56:12 2018
//
package main

import (
	"fmt"
	"sort"
)

type city struct {
	pref, year, no int
}

type cities []city

func (c cities) Len() int {
	return len(c)
}

func (c cities) Swap(i, j int) {
	c[i], c[j] = c[j], c[i]
}

func (c cities) Less(i, j int) bool {
	if c[i].pref == c[j].pref {
		return c[i].year < c[j].year
	}
	return c[i].pref < c[j].pref
}

func main() {
	var N, M int
	fmt.Scan(&N, &M)

	cs := make(cities, M)
	for i := range cs {
		fmt.Scan(&cs[i].pref, &cs[i].year)
	}

	cs2 := make(cities, len(cs))
	copy(cs2, cs)
	sort.Sort(cs)

	count := 1
	for i := range cs {
		if i > 0 && cs[i-1].pref != cs[i].pref {
			count = 1
		}
		cs[i].no = count
		count++
	}

	for _, c := range cs2 {
		lower := sort.Search(len(cs), func(i int) bool {
			return cs[i].pref >= c.pref
		})
		upper := sort.Search(len(cs), func(i int) bool {
			return cs[i].pref >= c.pref+1
		})
		fmt.Println(c, lower, upper)
		prefs := cs[lower:upper]

		index := sort.Search(len(prefs), func(i int) bool {
			return prefs[i].year >= c.year
		})
		fmt.Printf("%06d%06d\n", prefs[index].pref, prefs[index].no)
	}
}