#include<iostream>
#include<algorithm>
#define x first
#define y second
using namespace std;

const int N=110;

typedef pair<int,int> pii;

int num,m;
pii a[N];

bool cmp(pii c,pii d)
{
    return c.x<d.x;
}

int main()
{
    cin>>num>>m;
    int res=num+1;
    for(int i=0;i<m;i++)
    cin>>a[i].x>>a[i].y;
    sort(a,a+m,cmp);
    int l=a[0].x,r=a[0].y;
    for(int i=1;i<m;i++)
    {
        if(a[i].x<=r)
        r=max(a[i].y,r);
        else
        {
            res-=(r-l+1);
            l=a[i].x;
            r=a[i].y;
        }
    }
    res-=(r-l+1);
    cout<<res;
    return 0;
}