#include<bits/stdc++.h>
using namespace std;
long long n,k,a[1000008],ans=-1;
int main()
{
	cin>>n>>k;
	for(int i=1;i<=n;i++)
	{
		int x,b;
		cin>>x>>b;
		a[x]+=b;
	}
	for(long long i=0;i<=1000000-k;i++)
	{
		if(a[i]!=0&&a[i+k]!=0)
		{
			ans=max(ans,(i+i+k)*min(a[i],a[i+k]));
		}
	}
	if(ans==-1)cout<<"NO"<<endl;
	else cout<<ans<<endl;
	return 0;
}