#include<bits/stdc++.h>
using namespace std;
long long n,m,x[100100],y[100100],s;
int main()
{
//	freopen(".in","r",stdin);
//	freopen(".out","w",stdout);
    cin>>n>>m;
	for(int i=1;i<=n;i++)
	{
		cin>>x[i]>>y[i];
		s+=abs(x[i]-y[i]);
	 } 
	 sort(x+1,x+1+n);
	 sort(y+1,y+1+n);
	 for(int i=1;i<=n;i++)
	 s+=abs(x[i]-y[i]);
	 cout<<s+m;
//	fclose(stdin);
//	fclose(stdout);
	return 0;
}