#include <iostream>
#include <vector>

using namespace std;

long long n, m, i, a, b, db;

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);

    cin >> n >> m;

    vector <long long> x(n + 1);

    for (i = 1; i <= m; ++i)
    {
        cin >> a >> b;
        ++x[a];
        --x[b];
    }

    for (i=2; i<=n; ++i)
    {
        x[i]+=x[i-1];
    }

    x[0]=1;

    for (i=1; i<=n; ++i)
    {
        if (x[i-1]>0 && x[i]==0) ++db;
    }

    cout << db;
}