#include <iostream>
//#include <fstream>
#include <vector>
#include <algorithm>

#define ll long long

using namespace std;

//ifstream cin("aruszallitas.in");
//ofstream cout("aruszallitas.out");

vector<ll>x;

ll aa,bb,db,i,n,m,a,b;

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

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


    return 0;
}