#include<iostream>
#include<cstdio>
#include<bits/stdc++.h>
using namespace std;
int n,m,i,j,x[10050],y[10050],ans,s[10050];
int main(){
	cin>>n>>m;
	for(i=1;i<=n+1;i++){
		s[i]=0;
	}
	for(i=1;i<=m;i++){
		cin>>x[i]>>y[i];
		for(j=x[i];j<=y[i];j++){
			s[j]=1;
		}
	}
	for(i=1;i<=n+1;i++){
		if(s[i]==0) ans++;
	}
	cout<<ans;
}