/******************************************************************************

                              Online C++ Compiler.
               Code, Compile, Run and Debug C++ program online.
Write your code in this editor and press "Run" button to compile and execute it.

*******************************************************************************/

#include <iostream>

using namespace std;

typedef long long ll;

ll N, M, a, b, r, valsum;
ll tomb[1000000];

int main()
{
    cin >> N >> M;
    for (ll m = 0; m < M; m++) {
        cin >> a >> b;
        a--; b--;
        tomb[a]++;
        tomb[b]--;
    }
    bool f = false;
    for (ll &val : tomb) {
        valsum += val;
        if (valsum == 0 && !f) {
            r++;
            f = true;
        }
        else if (val != 0) {
            f = false;
        }
    }
    cout << r << endl;
}