import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################


class DualSegmentTree:
    def __init__(self, size, f, default):
        self.n = (size-1).bit_length()
        self.size = 1<<self.n
        self.default = default
        self.lazy = [default]*(self.size*2)
        self.f = f

    def propagate(self, k):
        lazy = self.lazy
        if lazy[k] != self.default:
            lazy[2*k] = self.f(lazy[2*k], lazy[k])
            lazy[2*k+1] = self.f(lazy[2*k+1], lazy[k])
            lazy[k] = self.default

    def thrust(self, k):
        for i in range(self.n,0,-1):
            self.propagate(k>>i)

    def update(self, a, b, x):
        a += self.size
        b += self.size-1
        self.thrust(a)
        self.thrust(b)
        l = a
        r = b + 1
        lazy = self.lazy
        while l < r:
            if l & 1:
                lazy[l] = self.f(lazy[l], x)
                l += 1
            if r & 1:
                r -= 1
                lazy[r] = self.f(lazy[r], x)
            l >>= 1
            r >>= 1
    
    def get(self, k):
        k += self.size
        self.thrust(k)
        return self.lazy[k]
n,m = na()
g = [na() for i in range(m)]
s = set()
for i in range(m):
    s.add(g[i][0])
    s.add(g[i][1])

d = {x:i for i, x in enumerate(sorted(s))}
for i in range(m):
    g[i] = [d[g[i][0]],d[g[i][1]]]
g = sorted(g,key = lambda x:x[1])

k = len(s)
inf = float("inf")
st = DualSegmentTree(k+1,max,-inf)
st.update(0,k+1,0)
for i in range(m):
    l,r = g[i]
    x = st.get(l)
    st.update(r,k+1,x + 1)
print(2*(n-1)-st.get(k))