#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #ifdef LOCAL # include "debug_print.hpp" # define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__) #else # define debug(...) (static_cast(0)) #endif using namespace std; #define rep(i,n) for(int i=0; i<(n); i++) #define rrep(i,n) for(int i=(n)-1; i>=0; i--) #define FOR(i,a,b) for(int i=(a); i<(b); i++) #define RFOR(i,a,b) for(int i=(b-1); i>=(a); i--) #define ALL(v) v.begin(), v.end() #define RALL(v) v.rbegin(), v.rend() #define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() ); #define pb push_back using ll = long long; using D = double; using LD = long double; using P = pair; template using PQ = priority_queue>; template using minPQ = priority_queue, greater>; templatebool chmax(T &a, const T &b) { if (abool chmin(T &a, const T &b) { if (b ostream &operator<<(ostream &os, const pair &p) { os << p.first << " " << p.second; return os; } template istream &operator>>(istream &is, pair &p) { is >> p.first >> p.second; return is; } template ostream &operator<<(ostream &os, const vector &v) { int s = (int)v.size(); for (int i = 0; i < s; i++) os << (i ? " " : "") << v[i]; return os; } template istream &operator>>(istream &is, vector &v) { for (auto &x : v) is >> x; return is; } void in() {} template void in(T &t, U &...u) { cin >> t; in(u...); } void out() { cout << "\n"; } template void out(const T &t, const U &...u) { cout << t; if (sizeof...(u)) cout << sep; out(u...); } void outr() {} template void outr(const T &t, const U &...u) { cout << t; outr(u...); } int main(){ ios_base::sync_with_stdio(false); cin.tie(nullptr); int n,m; in(n,m); vector s; vector> r; rep(i,m){ int a,b; in(a,b); s.emplace_back(a-1); s.emplace_back(b-1); r.emplace_back(a-1,b-1,0); } sort(ALL(s)); UNIQUE(s); sort(ALL(r)); int l = s.size(); rep(i,l-1) r.emplace_back(s[i], s[i+1],1); vector ans(l); rep(i,l) ans[i] = s[i]*2; for(auto [from, to, idx] : r){ int fi = lower_bound(ALL(s),from) - s.begin(); int ti = lower_bound(ALL(s),to) - s.begin(); if(idx == 0) chmin(ans[ti], ans[fi]+2*(to-from)-1); else chmin(ans[ti], ans[fi]+ 2*(to-from)); } ll res = ans.back() + 2*(n-1-s.back()); out(res); }