#include <iostream>
#include <vector>
using namespace std;

struct szallit{
    int fel,le,adb;
};

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

vector<szallit>x;

int main()
{
    cin>>n>>m;
    x.resize(n+1);
    for(i=1;i<=m;++i)
    {
        cin>>a>>b;
        ++x[a].fel;
        ++x[b].le;
    }
    x[0].adb=1;
    for(i=1;i<=n;++i)
    {
        if(i>1) x[i].adb=x[i-1].adb;
        if(x[i].fel!=0)x[i].adb+=x[i].fel;
        if(x[i].le!=0)x[i].adb-=x[i].le;
        if(x[i].adb==0 && x[i].adb!=x[i-1].adb && i!=n) ++db;
    }
    cout<<db;
    return 0;
}