#include<iostream>
using namespace std;
int main() {
	int i,j,l,m,u,v,s=0;
	int f[100001];
	cin >> l >> m;
	for (i=1;i<=l;i++)
	    f[i]=1;
	for (i=1;i<=m;i++){
		cin >> u >> v;
		for (j=u;j<=v;j++)
		    f[j]=0;
	}
	for (i=0;i<=l;i++)
	    s=s+f[i];
	cout << s;
	return 0; 
}