#include<iostream>

#include<vector>

#include<algorithm>

using namespace std;

int s[];

int main(){

    int L, M;

    cin >> L >> M;

    int l, r;

    for(int i = ; i < M; i++){

        cin >> l >> r;

        s[l] = max(s[l], r - l + );

    }

    int res = L + ;

    int now = ;

    for(int i = ; i <= L; i++){

        now = max(now, s[i]);

        if(now != ){

            res--;

            now--;

        }

    }

    cout << res << endl;

    return ;

}