#include <iostream>
#include <cstdio>
#include <cmath>
#include <map>
#include <vector>
#include <algorithm>
#include <string>
#include <cstring>
#define int long long
using namespace std;
signed main(){
    int l,m,q,z;
    cin>>l>>m;
    int c=l+1,a[l+1]={1};
    while(m){
        
        scanf("%d%d",&q,&z);
        for(int i=q;i<=z;i++){
            if(a[i]==1){
                --c;
                a[i]=0;
            }
        }
        m--;
    }
    cout<<c;
    return 0;
}