文件目录

#include <iostream>
using namespace std;
int main()
{
    int l, m, u, v;
    int t[10050] = {};
    cin >> l >> m;
    int c = 0;
    while (m--)
    {
        cin >> u >> v;
        for (int i = u; i <= v; i++)
            if (t[i] == 0)
            {
                t[i] = 1;
                c++;
            }
    }
    cout << l + 1 - c;
    return 0;
}