#include <bits/stdc++.h>
using namespace std;


void solve(){
    int n, m;
    cin>>n>>m;
    vector<pair<int,int>> a(m);
    for(int i=0; i<m; i++){
        cin>>a[i].first>>a[i].second;
    }
    sort(a.begin(), a.end());
    int covered=a[0].second, ans=a[0].first-1;
    for(int i=1; i<m; i++){
        if(a[i].first>covered){
            ans+=a[i].first-covered;
        }
        covered=max(a[i].second, covered);
    }
    cout<<ans<<"\n";
}

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    solve();
    return 0;
}