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

struct abrakadabra{
    int fel,le,adb;
};

int n,m;
vector<abrakadabra>x;

int main()
{
    cin >> n >> m;

    // Use emplace_back to construct elements in place in the vector
    x.resize(n+1);
    for (int i = 1; i <= m; ++i)
    {
        int a, b;
        cin >> a >> b;
        x[a].fel++;
        x[b].le++;
    }

    x[0].adb = 1;
    int db = 0;
    for (int i = 1; i <= n; ++i)
    {
        if (i > 1)
            x[i].adb = x[i-1].adb;
        if (x[i].fel != 0)
            x[i].adb += x[i].fel;
        if (x[i].le != 0)
            x[i].adb -= x[i].le;
        if (x[i].adb == 0 && x[i].adb != x[i-1].adb && i != n)
            db++;
    }

    cout << db;
    return 0;
}