#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
  int N,M;
  cin>>N>>M;
  vector<pair<int,int>> S(M);
  int x;
  for(int i=0;i<M;i++){
      int a,b;
      cin>>a>>b;
      S[i] = {b,a};
  }
  sort(S.begin(),S.end());
  int now = S[0].second;
  int ans = 0;
  for(int i=1;i<M;i++){
      int b,a;
      tie(b,a) = S[i];
      if(now <= a){
          ans++;
          now = b;
      }
  }
  cout<<(N-1)*2-ans-1<<endl;
}