#include<bits/stdc++.h>
/*
#include<atcoder/all>
using namespace atcoder;
//using mint = modint1000000007;
using mint = modint998244353;
*/
//g++ -I/opt/ac-library ./**.cpp
using namespace std;
using ll = long long;
using ull = unsigned long long;
//const long long MOD = 1000000007;
const long long MOD = 998244353;
const long double PI = 3.14159265358979;
const long long INF = 1LL<<60;
template <typename T> bool chmax(T &a, const T& b){if(a < b){a = b;return true;}return false;}
template <typename T> bool chmin(T &a, const T& b){if(a > b){a = b;return true;}return false;}
#define deb(var) do{cout << #var << " : "; view(var);}while(0)
template<typename T> void view(T e){cout << e << endl;}
void view(vector<string>& v){cout << endl;for(auto& s :v){view(s);}cout << endl;}
template<typename T> void view(vector<T>& v){for(auto& e :v){cout << e << " ";}cout << endl;}
template<typename T> void view(vector<vector<T>>& vv){cout << endl;for(auto& v:vv){view(v);}}
ll gcd(ll a, ll b){if (b == 0) return a;else return gcd(b, a % b);}
ll lcm(ll x,ll y){return ll(x/gcd(x,y))*y;}
template<typename T> using min_priority_queue = priority_queue<T, vector<T>, greater<T>>;
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define int long long

template<class T>
struct compress{
    vector<int> res;
    vector<T> comp, A_copy;
    int n;
    int siz; //圧縮後の種類数
    compress(vector<T>& A){
        n = A.size();
        res.resize(n);
        comp = A;
        A_copy = A;
        init();
    }

    void init(){
        sort(comp.begin(), comp.end());
        comp.erase(unique(comp.begin(), comp.end()), comp.end());
        siz = comp.size();
        for(int i=0; i<n; i++){
            res[i] = lower_bound(comp.begin(), comp.end(), A_copy[i]) - comp.begin();
        }
    }

    //座圧後の最大値
    int max() {
        return comp.size()-1;
    }

    //圧縮後の値を渡すと元の値を返す．
    T raw(int a){
        return comp[a];
    }

    //座圧前の値を座圧後の値に変換
    int press(T a) {
        return lower_bound(comp.begin(), comp.end(), a) - comp.begin();
    }
};

int32_t main() {
    int n, m; cin >> n >> m;
    vector<pair<int, int>> I(m);
    vector<int> v;
    for (int i=0; i<m; i++) {
        int a, b; cin >> a >> b; a--; b--;
        I[i] = {a, b};
        v.push_back(a);
        v.push_back(b);
    }
    compress<int> C(v);
    for (int i=0; i<m; i++) {
        I[i] = {C.press(I[i].first), C.press(I[i].second)};
    }
    int mx = C.max();
    sort(all(I), [&] (pair<int, int> a, pair<int, int> b) {
        return a.second < b.second;
        return a.first < b.first;
        return true;
    });

    vector<int> dp(mx + 1, 0);
    int best = 0;
    for (auto [a, b] : I) {
        chmax(dp[b], best);
        chmax(dp[b], dp[a] + 1);
        chmax(best, dp[b]);
    }
    int ans = 2 * (n - 1);
    int res = 0;
    cout << ans - best << "\n";
}