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

using namespace std;

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

vector <int> x;

int n,m,a,b,i,db,rdb;

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

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

        else if(x[i]!=0 && db>0)
            ++rdb;
    }
    //for(auto &e:x) cout<<e<<" ";
    cout<<rdb;
    return 0;
}