#include<bits/stdc++.h>
using namespace std;
int main(){
	int m,l,t[10005]={},g=0;
	cin>>l>>m;
	for(int i=0;i<m;i++){
		int s,n;
		cin>>s>>n;
        if(s>n) swap(s,n);
		for(int j=s;j<=n;j++) t[j]=1;
	}
	for(int i=0;i<=l;i++){
		if(t[i]==0) g++;
	}
	cout<<g;
}
/**************************************************************
	Problem: 1470
	User: wangyiyang
	Language: C++
	Result: Accepted
	Time:43 ms
	Memory:2072 kb
****************************************************************/