#include <bits/stdc++.h>
using namespace std;

int main(){
	//有树标记为0，没有树标记为-1 
	int l,m,a[10010] = {0},i,x,y,c = 0,j;
	cin>>l>>m;
	for(i = 1;i <= m;i++){
		cin>>x>>y;
		for(j = x;j <= y;j++){
			if(a[j] == 0){
				a[j] = -1;
				c++;	
			}
		}
	}
	
	cout<<l+1-c;
}
/**************************************************************
	Problem: 1470
	User: admin
	Language: C++
	Result: Accepted
	Time:51 ms
	Memory:2072 kb
****************************************************************/