#include <stdio.h>
#include <fstream>
#include <iostream>
#include <stdlib.h>
#include <list>

using namespace std;

class gutui_t {
	public:
		int h;
		int g;
		float x;
	public:
		gutui_t(int hval, int gval);
		gutui_t(){
			h = 0;
			g = 0;
			x = 0;
		}
		~gutui_t(){}
}; 
gutui_t::gutui_t (int hval, int gval){
	h = hval;
	g = gval;
	x = 0;
}


fstream f("gutui.in",ios::in);
fstream out("gutui.out",ios::out);

bool compare (gutui_t fst, gutui_t snd)
{
	if ( fst.x > snd.x)
		return true;
	if (fst.x == snd.x && fst.h > snd.h)
		return true;
	return false;
}


int main(){
	int n, hmax, u, i, size;
	list <gutui_t> v;
	gutui_t gutuie;
	int h, g, val = 0;   

	f>>n;
	f>>hmax;
	f>>u;
	for (i = 0; i< n; i++){
		f>>h>>g;
		gutuie.h = h;
		gutuie.g = g;
		if( h <= hmax){
			gutuie.x = (float)gutuie.g / (hmax - gutuie.h); 
			v.push_back(gutuie);
		}
	}

	i = 0;
	while( !v.empty()){
		
		i=0;
		v.sort(compare);
		gutuie = v.front();
		v.pop_front();
		val += gutuie.g;
		size = v.size();
		while( i < size){
			gutuie = v.front();
			v.pop_front();
			gutuie.h += u;
			if (gutuie.h <=hmax ){
				if(gutuie.h <hmax) gutuie.x =  (float)gutuie.g / (hmax - gutuie.h); 
				if(gutuie.h == hmax) gutuie.x =  gutuie.g;
				v.push_back(gutuie);
			}
			i++;
		}
		
	}

	out<<val;
	return 0;
}