#include <iostream>
#include <fstream>
using namespace std;
int oi[5000];
int main()
{
	ifstream f("lupu.in");
	int n,x,l,d,a,pasi,i;
	long long s=0;
	f >> n >> x >> l;
	for (i = 0;i<n;i++)
	{
		f >> d >> a;
		pasi = (x-d)/l + 1;
		if (oi[pasi] < a)
			oi[pasi] = a;
	}
	for (i = 0;i<n;i++)
		s += oi[i];
	ofstream g("lupu.out");
	g << s << endl;
}