// UUID: 48f6183f-0600-4976-a8ea-f0476b67cf9f
#include <bits/stdc++.h>
using usll = unsigned long long;
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    
    int n = 0, m = 0, sum = 0;
    cin >> n >> m;
    vector<bool> szakasz(n+1, false); //x -től x+1 -ig

    for(int i = 0; i < m; i++) {
        int a,b;
        cin >> a >> b;
        for(int j = a; j < b; j++) {
            szakasz[j] = true;
        }
    }

    bool prev = false;
    for(int i = 0; i < n; i++) {
        if (prev && !szakasz[i]) sum++;
        prev = szakasz[i];
    }
    
    cout << sum << '\n';
    return 0;
}