#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000001

int main(){
	
	int N,M;
	cin>>N>>M;
	
	long long ans = N-1;
	ans *= 2;
	
	vector<int> a(M),b(M);
	vector<pair<int,int>> t;
	rep(i,M){
		cin>>a[i]>>b[i];
		
		t.emplace_back(b[i],a[i]);
	}
	
	sort(t.begin(),t.end());
	int cur =-1;
	
	rep(i,t.size()){
		if(t[i].second>=cur){
			cur = t[i].first;
			ans --;
		}
	}
	
	cout<<ans<<endl;
	
	
	
    return 0;
}