#include<iostream>
using namespace std;
int main()
{
  int l,m,sum=0;
  int i,qi,zhi;
  int temp[10001]={0};
  cin>>l>>m;
  while(m--)
  {
   
   cin>>qi>>zhi;
   for(i=qi;i<=zhi;i++)
      if(temp[i]==0) {temp[i]=1;sum++;}
   }                              
   cout<<(1+l-sum)<<endl; 
 return 0;  
    
}