#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;

int main(){
	ifstream f("lupu.in");
	int n, x, l;
	f >> n >> x >> l;
	vector<pair<int, int> > oi;
	oi.resize(n);
	int dist, ultima_tura = 0;
	for(auto& oaie : oi){
		f >> dist;
		f >> oaie.second;
		oaie.first = (x - dist)/l;
		if(ultima_tura < oaie.first){
			ultima_tura = oaie.first; } }
	sort(begin(oi), end(oi), [](const pair<int, int>& lhs, const pair<int, int>& rhs){
		return (lhs.first == rhs.first) ? (lhs.second > rhs.second) : lhs.first > rhs.first; });
	int tura_curenta = ultima_tura, rez = 0;
	for(const auto& x : oi){
		if(tura_curenta < 0){
			goto out; }
		if(tura_curenta <= x.first){
			rez += x.second;
			--tura_curenta; } }
	out:
	ofstream g("lupu.out");
	g << rez;
	return 0; }