#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
using namespace std;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    #define int long long
    int n, m; cin >> n >> m;
    set<int> path;
    for (int i = 0; i < n; i++) {
        path.insert(i + 1);
    }
    for (int i = 0; i < m; i++) {
        int from, to;
        cin >> from >> to;
        for (int j = from; j <= to; j++) {
            path.erase(j);
        }
    }
    cout << path.size();
}
//10 4
//8 9
//1 6
//1 3
//3 4