#include <iostream>
#include <bits/stdc++.h>

using namespace std;
/*
10 4
8 9
1 6
1 3
3 4
*/
int main()
{
    int n, q; cin >> n >> q;
    vector<int> delta(n + 1, 0);
    for(int i = 0; i < q; i++){
        int a, b; cin >> a >> b;
        delta[a]++;
        delta[b]--;
    }
    delta[0] = 1;
    int counter = 0;
    vector<int> packs(n + 1, 0);
    for(int i = 1; i <= n; i++){
        packs[i] = packs[i - 1] + delta[i];
    }
    for(int i = 1; i <= n - 1; i++){
        if(packs[i] == 0 and packs[i - 1] != 0){
            counter++;
        }
    }
    cout << counter;
}