#include <iostream>
#include <vector>

using namespace std;

int main()
{
    int N, M;
    cin >> N >> M;

    vector <bool> szallitas(N+1, false);
    szallitas[0] = true;

    for (int i = 1; i <= M; i++) {
        int x,y;
        cin >> x >> y;
        for (int j = x; j <= y; j++) { szallitas[j] = true; }
    }

    int db = 0;
    for (int i = 1; i <= N; i++) {
        if (szallitas[i] == false && szallitas[i-1] == true) {db++;}
    }

    cout << db;
    return 0;
}