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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;

class Program
{
	public static int Main(string[] args)
	{
		string[] str = Console.ReadLine().Split(' ');
		int n = int.Parse(str[0]);
		int m = int.Parse(str[1]);
		int a = 0;
		int b = 0;
		int bMin = n;
		int sum = 1;
		for (int i = 0; i < m;i++){
			string[] input = Console.ReadLine().Split(' ');
			b = int.Parse(input[1]);
			if(a < int.Parse(input[0])){
				a = int.Parse(input[0]);
				if (bMin <= b) {
					sum++;
					bMin = b;
				}
			}
			else{
				if(b > int.Parse(input[1])){
					bMin = int.Parse(input[1]);
				}					
			}

		}
		Console.WriteLine(sum);
		return 0;
	}
}