#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef int64_t lint;
#define rep(i, n) for(int i=0; i<n; i++)
#define repx(i, l, n) for(int i=l; i<n; i++)
#define all(v) v.begin(), v.end()
#define show(x) cout << #x << ": " << x << endl;
#define list(x) cout << #x << ": " << x << "  ";
#define pb push_back
using vi = vector<lint>;
using vvi = vector<vector<lint>>;
template<class T> inline void vin(vector<T>& v) { rep(i, v.size()) cin >> v.at(i); }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T> inline void drop(T x) { cout << x << endl; exit(0); }
template<class T> void vout(vector<T> v) { rep(i, v.size()) { cout << v.at(i) << ' '; } cout << endl; }
constexpr lint LINF = LLONG_MAX/2;
template<class T> map<T, int> coord_comp(set<T> s) {
	int a = 0;
	map<T, int> m;
	for (auto u : s) m[u] = ++a;
	return m;
}

int main() {
	lint N, M;
	cin >> N >> M;
	vi v(M), w(M);
	rep(i, M) cin >> v[i] >> w[i];

	lint a=0, b=0, c=0, x, y, z;
	vvi G(2*M+1);
	set<lint> s;
	rep(i, M) {
		s.insert(v[i]);
		s.insert(w[i]);
	}
	map<lint, int> m = coord_comp(s);
	rep(i, M) {
		G[m[v[i]]].pb(m[w[i]]);
	}
	vi dp(2*M+1);
	rep(i, 2*M) {
		chmax(dp[i+1], dp[i]);
		rep(j, G[i].size()) {
			chmax(dp[G[i][j]], dp[i]+1);
		}
	}
	std::cout << 2*N-2-dp[2*M] << '\n';
}