#line 1 "main.cpp"
#pragma region Macros
#include <bits/stdc++.h>
using namespace std;
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;
}
#ifdef DEBUG
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
    os << '{';
    for(int i = 0; i < (int)v.size(); i++) {
        if(i) { os << ','; }
        os << v[i];
    }
    os << '}';
    return os;
}
void debugg() { cerr << endl; }
template <class T, class... Args>
void debugg(const T &x, const Args &... args) {
    cerr << " " << x;
    debugg(args...);
}
#define debug(...)                                                             \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]: ", debugg(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif

struct Setup {
    Setup() {
        cin.tie(0);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(15);
    }
} __Setup;

using ll = long long;
#define OVERLOAD3(_1, _2, _3, name, ...) name
#define ALL(v) (v).begin(), (v).end()
#define RALL(v) (v).rbegin(), (v).rend()
#define REP1(i, n) for(int i = 0; i < int(n); i++)
#define REP2(i, a, b) for(int i = (a); i < int(b); i++)
#define REP(...) OVERLOAD3(__VA_ARGS__, REP2, REP1)(__VA_ARGS__)
#define UNIQUE(v) sort(ALL(v)), (v).erase(unique(ALL(v)), (v).end())
#define SZ(v) ((int)(v).size())
const int INF = 1 << 30;
const ll LLINF = 1LL << 60;
constexpr int MOD = 1000000007;
constexpr int MOD2 = 998244353;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

void Case(int i) { cout << "Case #" << i << ": "; }
int popcount(int x) { return __builtin_popcount(x); }
ll popcount(ll x) { return __builtin_popcountll(x); }
#pragma endregion Macros

#line 1 "/Users/siro53/kyo-pro/compro_library/data_structure/compress.hpp"
template <typename T> struct Compress {
    vector<T> v;
    Compress() {}
    Compress(vector<T> vv) : v(vv) {
        sort(ALL(v));
        v.erase(unique(ALL(v)), end(v));
    }
    void build(vector<T> vv) {
        v = vv;
        sort(ALL(v));
        v.erase(unique(ALL(v)), end(v));
    }
    int get(T x) { return (int)(lower_bound(ALL(v), x) - v.begin()); }
    T &operator[](int i) { return v[i]; }
    size_t size() { return v.size(); }
};
#line 77 "main.cpp"

int main() {
    int N, M;
    cin >> N >> M;
    vector<int> tmp;
    vector<pair<int, int>> edges(M);
    for(auto& [a, b] : edges) {
        cin >> a >> b;
        tmp.push_back(a);
        tmp.push_back(b);
    }
    tmp.push_back(1);
    tmp.push_back(N);
    Compress<int> comp(tmp);
    int V = SZ(comp);
    vector<vector<pair<int, ll>>> G(V);
    REP(i, V-1) {
        ll d = ll(comp[i+1] - comp[i]) * 2;
        G[i].emplace_back(i+1, d);
    } 
    for(auto [a, b] : edges) {
        int pa = comp.get(a);
        int pb = comp.get(b);
        ll d = 2LL * b - 2LL * a - 1;
        G[pa].emplace_back(pb, d);
    }
    vector<ll> dp(V, LLINF);
    dp[0] = 0;
    priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll, int>>> que;
    que.emplace(0, 0);
    while(!que.empty()) {
        auto [d, u] = que.top();
        que.pop();
        if(d > dp[u]) continue;
        for(auto [v, x] : G[u]) {
            if(chmin(dp[v], d + x)) {
                que.emplace(dp[v], v);
            }
        }
    }
    cout << dp.back() << endl;
}