class SegTree:
    def __init__(self, n, e, ope, lst=[]):
        self.N0 = 2 ** (n - 1).bit_length()
        self.e = e
        self.ope = ope
        self.data = [e] * (2 * self.N0)
        if lst:
            for i in range(n):
                self.data[self.N0 + i] = lst[i]
            for i in range(self.N0 - 1, 0, -1):
                self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])
    
    def build(self):
        for i in range(self.N0 - 1, 0, -1):
            self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])
                
    def update(self, i, x): #a_iの値をxに更新
        i += self.N0
        self.data[i] = x
        while i > 1:
            i >>= 1
            self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])
    
    def add(self, i, x):
        self.update(i, x + self.get(i))

    def set(self, i, x):
        self.data[self.N0 + i] = x
    
    def query(self, l, r): #区間[l, r)での演算結果
        if r <= l:
            return self.e
        lres = self.e
        rres = self.e
        l += self.N0
        r += self.N0
        while l < r:
            if l & 1:
                lres = self.ope(lres, self.data[l])
                l += 1
            if r & 1:
                r -= 1
                rres = self.ope(self.data[r], rres)
            l >>= 1
            r >>= 1
        return self.ope(lres, rres)
    
    def get(self, i): #a_iの値を返す
        return self.data[self.N0 + i]

n, m = map(int, input().split())
se = set()
ab = [list(map(int, input().split())) for _ in range(m)]
for a, b in ab:
    se.add(a)
    se.add(b)
se.add(1)
le = len(se)
lst = sorted(se)
dic = {l:i for i, l in enumerate(lst)}
R = [[] for _ in range(le)]
for a, b in ab:
    a = dic[a]
    b = dic[b]
    R[b].append(a)
seg = SegTree(le, -1 << 30, max)
seg.update(0, 0)
for r in range(le):
    for l in R[r]:
        tmp = seg.query(0, l + 1) + 1
        if seg.get(r) < tmp:
            seg.update(r, tmp)
print(2 * (n - 1) - seg.query(0, le))