#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<long long,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n, m; cin >> n >> m;
	map<int, vector<int>>mp;
	vector<int>v;
	rep(i, m) {
		int a, b; cin >> a >> b; a--; b--;
		v.push_back(a);
		v.push_back(b);
		mp[b].push_back(a);
	}
	v.push_back(0);
	v.push_back(n - 1);
	sort(all(v));
	v.erase(unique(all(v)), v.end());
	map<int, int>dp;
	dp[0] = 0;
	rep2(i, 1, v.size()) {
		int d = dp[v[i - 1]] + (v[i] - v[i - 1]) * 2;
		for (auto e : mp[v[i]]) {
			chmin(d, dp[e] + 2 * (v[i] - e) - 1);
		}
		dp[v[i]] = d;
	}
	/*for (auto e : dp) {
		cout << e.first << " " << e.second << endl;
	}*/
	cout << dp[n - 1] << endl;
	return 0;
}