#include <bits/stdc++.h>
using namespace std;
int main(){
  int N, M;
  cin >> N >> M;
  vector<int> A(M), B(M);
  for (int i = 0; i < M; i++){
    cin >> A[i] >> B[i];
  }
  vector<pair<int, int>> P(M);
  for (int i = 0; i < M; i++){
    P[i] = make_pair(B[i], A[i]);
  }
  sort(P.begin(), P.end());
  int q = 0;
  int c = 0;
  for (int i = 0; i < M; i++){
    if (q <= P[i].second){
      q = P[i].first;
      c++;
    }
  }
  cout << (N - 1) * 2 - c << endl;
}