Problem:
Score : 400 points

Problem Statement

There are N islands lining up from west to east, connected by N-1 bridges.

The i-th bridge connects the i-th island from the west and the (i+1)-th island from the west.

One day, disputes took place between some islands, and there were M requests from the inhabitants of the islands:

Request i: A dispute took place between the a_i-th island from the west and the b_i-th island from the west. Please make traveling between these islands with bridges impossible.

You decided to remove some bridges to meet all these M requests.

Find the minimum number of bridges that must be removed.

Constraints

All values in input are integers.

2 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq a_i < b_i \leq N

All pairs (a_i, b_i) are distinct.

Input

Input is given from Standard Input in the following format:

N M
a_1 b_1
a_2 b_2
:
a_M b_M

Output

Print the minimum number of bridges that must be removed.

Sample Input 1

5 2
1 4
2 5

Sample Output 1

1

The requests can be met by removing the bridge connecting the second and third islands from the west.

Sample Input 2

9 5
1 8
2 7
3 5
4 6
7 9

Sample Output 2

2

Sample Input 3

5 10
1 2
1 3
1 4
1 5
2 3
2 4
2 5
3 4
3 5
4 5

Sample Output 3

4

Solution in Go (1.6) (judge verdict: Wrong Answer)

package main
import (
  "fmt"
    "sort"
)

func main() {

  var n,m int
  var keys  []int
  fmt.Scan(&n,&m)
  var list = make( map[int]int)
  for i := 0 ; i < m; i++ {
  
    var ta,tb int
    fmt.Scan(&ta,&tb)
    keys = append(keys,tb)
    list[tb]=ta
  }
  sort.Ints(keys)
  var result,temp int = 0,0
  for i:= 0; i < m ; i++ {
    if !(list[keys[i]] <=temp && temp < keys[i] ) {
      temp = keys[i]-1
      result += 1
    }  

  }
  
  fmt.Print(result)
  
}