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 Python (3.4.3) (judge verdict: Wrong Answer)

ip1 = input().split()
M = int(ip1[1])
buf = []
def conf(char):
    data = []
    ip = char.split()
    for i in ip:
        data.append(int(i))
    return data

buf.append(conf(input()))

for i in range(M-1):
    order = conf(input())
    for j in range(len(buf)):
        if buf[j][0] < order[0] and buf[j][1] > order[0]:
            buf[j][0] = order[0]
        elif buf[j][0] > order[1] and buf[j][1] < order[1]:
            buf[j][1] = order[1]
        elif buf[j][0] > order[1] and buf[j][1] < order[0]:
            buf.append(order)

print(len(buf))