import sys
#input = sys.stdin.readline
#input = sys.stdin.buffer.readline #文字列はダメ
#sys.setrecursionlimit(1000000)
#import bisect
#import itertools
#import random
#from heapq import heapify, heappop, heappush
#from collections import defaultdict 
#from collections import deque
#import copy
#import math
#from functools import lru_cache
#@lru_cache(maxsize=None)
#MOD = pow(10,9) + 7
#MOD = 998244353
#dx = [1,0,-1,0]
#dy = [0,1,0,-1]
#dx8 = [1,1,0,-1,-1,-1,0,1]
#dy8 = [0,1,1,1,0,-1,-1,-1]

#和のセグ木にするときは以下の関数を定義する必要あり。
def segfunc(x,y):
  return x+y

class SegmentTree(object):
    def __init__(self, A, dot, unit):
        n = 1 << (len(A) - 1).bit_length()
        tree = [unit] * (2 * n)
        for i, v in enumerate(A):
            tree[i + n] = v
        for i in range(n - 1, 0, -1):
            tree[i] = dot(tree[i << 1], tree[i << 1 | 1])
        self._n = n
        self._tree = tree
        self._dot = dot
        self._unit = unit

    def __getitem__(self, i):
        return self._tree[i + self._n]

    def update(self, i, v):
        i += self._n
        self._tree[i] = v
        while i != 1:
            i >>= 1
            self._tree[i] = self._dot(self._tree[i << 1], self._tree[i << 1 | 1])

    def add(self, i, v):
        self.update(i, self[i] + v)

    def sum(self, l, r): #これで[l,r)から取り出す。
        l += self._n
        r += self._n
        l_val = r_val = self._unit
        while l < r:
            if l & 1:
                l_val = self._dot(l_val, self._tree[l])
                l += 1
            if r & 1:
                r -= 1
                r_val = self._dot(self._tree[r], r_val)
            l >>= 1
            r >>= 1
        return self._dot(l_val, r_val)

def compress(S):
    S = set(S); S = list(S)
    S.sort()
    dic_comp_ori = {}
    dic_ori_comp = {}
    for i,a in enumerate(S):
        dic_ori_comp[a] = i
        dic_comp_ori[i] = a
    return dic_comp_ori, dic_ori_comp 

def main():
    N,M = map(int,input().split()); INF = pow(10,18)
    roads = []
    S = set([])
    for _ in range(M):
        A,B = map(int,input().split())
        S.add(A)
        S.add(B)
        roads.append((A,B))

    dic_comp_ori, dic_ori_comp = compress(S)
    for i,road in enumerate(roads):
        a = dic_ori_comp[road[0]]
        b = dic_ori_comp[road[1]]
        roads[i] = (a,b)
    oriN = N
    N = len(dic_ori_comp)
    roads.sort(key=lambda x: x[1])
    #print(roads)
    
    Tree = SegmentTree([0]*N,max,0)
    for s,t in roads:
        v = Tree.sum(0,s+1) + 1 #[0,s]
        Tree.update(t, max(Tree[t],v))
    
    ans = (oriN-1)*2 - Tree.sum(0,N)
    print(ans)

if __name__ == '__main__':
    main()