#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
// #include <atcoder/modint>
// #include <atcoder/fenwicktree>
// #include <atcoder/segtree>
// #include <atcoder/scc>

#define int long long
#define all(x) begin(x), end(x)

using namespace std;
// using namespace atcoder;
// using mint = modint998244353;
// using mint = modint1000000007;
using ld = long double;
using pii = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vp = vector<pii>;
using vvp = vector<vp>;
using vs = vector<string>;
using vvc = vector<vector<char>>;

void debug(vector<int> a) {
    for (auto x : a) cout << x << ' ';
    cout << endl;
}

void debug(vector<vector<int>> a) {
    for (auto y : a) debug(y);
}

template <typename T1, typename T2>
inline bool chmax(T1 &a, T2 b) {return a < b and (a = b, true);}

template <typename T1, typename T2>
inline bool chmin(T1 &a, T2 b) {return a > b and (a = b, true);}

const int supl = LONG_LONG_MAX - 100;

template <typename T>
vector<int> compress(const vector<T>& a) {
    vector<T> cp = a;
    sort(cp.begin(), cp.end());
    cp.erase(unique(cp.begin(), cp.end()), cp.end());
    vector<int> res(a.size());
    for (int i = 0 ; i < a.size() ; i++) res[i] = lower_bound(cp.begin(), cp.end(), a[i]) - cp.begin();
    return res;
}

void main_() {
    int n, m; cin >> n >> m;
    vp es(m); for (auto& [a, b] : es) cin >> a >> b;
    sort(all(es));
    map<int, int> comp;
    {
        set<int> st;
        for (auto [a, b] : es) {
            st.emplace(a);
            st.emplace(b);
        }
        st.emplace(n);
        int cnt = 0;
        for (auto x : st) {
            comp[x] = cnt++;
        }
    }

    // cout << endl;
    // for (auto [x, y] : comp) cout << x << ' ' << y << endl;
    // 
    vvi G(comp.size());
    for (auto [a, b] : es) G[comp[a]].emplace_back(comp[b]);
    // 
    // cout << endl;

    // debug(G);

    vi dp(comp.size());
    for (int i = 0 ; i < comp.size() ; i++) {
        for (auto x : G[i]) chmax(dp[x], dp[i] + 1);
        if (i != n - 1) chmax(dp[i + 1], dp[i]);
    }

    cout << 2*(n - 1) - dp.back() << endl;
}

signed main() {
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    main_();

    return 0;
}