#include <bits/stdc++.h>
using namespace std;
//*
#include <atcoder/all>
using namespace atcoder;
//using mint = modint998244353;
using mint = modint1000000007;
//*/
using ll = long long;
using ld = long double;
using pll = pair<ll, ll>;
using tlll = tuple<ll, ll, ll>;
constexpr ll INF = 1LL << 60;
template<class T> bool chmin(T& a, T b) {if (a > b) {a = b; return true;} return false;}
template<class T> bool chmax(T& a, T b) {if (a < b) {a = b; return true;} return false;}
ll safemod(ll A, ll M) {ll res = A % M; if (res < 0) res += M; return res;}
ll divfloor(ll A, ll B) {if (B < 0) {return divfloor(-A, -B);} return (A - safemod(A, B)) / B;}
ll divceil(ll A, ll B) {if (B < 0) {return divceil(-A, -B);} return divfloor(A + B - 1, B);}
ll mypowl(ll A, ll B) {ll res = 1; for (int i = 0; i < B; i++) {res *= A;} return res;}
template<class T> void unique(vector<T> &V) {V.erase(unique(V.begin(), V.end()), V.end());}
template<class T> void sortunique(vector<T> &V) {sort(V.begin(), V.end()); V.erase(unique(V.begin(), V.end()), V.end());}
#define FINALANS(A) do {cout << (A) << '\n'; exit(0);} while (false)
template<class T> void printvec(const vector<T> &V) {int _n = V.size(); for (int i = 0; i < _n; i++) cout << V[i] << (i == _n - 1 ? "" : " ");cout << '\n';}
template<class T> void printvect(const vector<T> &V) {for (auto v : V) cout << v << '\n';}
template<class T> void printvec2(const vector<vector<T>> &V) {for (auto &v : V) printvec(v);}

template <class T>
vector<T> zarts_light(const vector<T> &V, int cnt = 0)
{
  vector<T> W = vector<T>(V);
  sortunique(W);
  vector<T> res(V.size());
  for (int i = 0; i < (int)V.size(); i++)
  {
    res[i] = cnt + lower_bound(W.begin(), W.end(), V[i]) - W.begin();
  }
  return res;
}

int main()
{
  ll N, M;
  cin >> N >> M;
  vector<ll> C(2 * M);
  for (ll i = 0; i < 2 * M; i += 2)
  {
    cin >> C.at(i) >> C.at(i + 1);
  }
  C = zarts_light(C);

  vector<vector<ll>> G(2 * M);
  for (ll i = 0; i < 2 * M; i += 2)
  {
    G.at(C.at(i)).push_back(C.at(i + 1));
  }

  vector<ll> dp(2 * M, 0);
  for (ll i = 0; i < 2 * M; i++)
  {
    for (auto ni : G.at(i))
    {
      chmax(dp.at(ni), dp.at(i) + 1);
    }
    if (i != 2 * M - 1)
      chmax(dp.at(i + 1), dp.at(i));
  }

  ll ans = 2 * (N - 1) - dp.at(2 * M - 1);
  cout << ans << endl;
}