#include <iostream>

/* run this program using the console pauser or add your own getch, system("pause") or input loop /
using namespace std;
int main(int argc, char* argv)
{
int a,b,n,m,i,s=0,x[1100]={};
cin>>n>>m;
for(i=1;i<=n;i++)
{
cin>>a>>b;
}
for(i=a;i<=b;i++)
{
x[i]=1;
}
for(i=1;i<=n;i++)
if(x[i]!=1)
{
s++;
}
cout<<s;
return 0;
}