/**
 * Maruseac Andrei
 * 325 CC
 * Proiectarea Algoritmilor
 * Tema 1
 * Problema 2: gutui
 */

#include <stdio.h>
#include <stdlib.h>

int N;	/* numarul de gutui din copac */
int H;	/* inaltimea maxima la care se poate ajunge */
int U;	/* cu cat se ridica crengile dupa culegerea unui gutui */
int M;	/* greutatea maxima */

typedef struct gutui {
	int h;	/* inaltimea la care se afla gutuiul */
	int g;	/* greutatea gutuiului */
} gutui;

gutui gut[100001];

/**
 * functie de comparare a 2 gutui
 * a, b		elementele de comparat
 */
int comp (const void * a, const void * b)
{
	gutui * a1 = (gutui *) a;
	gutui * b1 = (gutui *) b;
	
	if (a1 -> h != b1 -> h)
		return b1 -> h - a1 -> h;
	else
		return b1 -> g - a1 -> g;
}

/**
 * functie de citire
 * file_name	nume fisier
 */
void read (char * file_name) 
{
	int i;

	FILE * fd = fopen (file_name, "r");
 
	// dimensiune matrice 
	fscanf (fd, "%d", &N);
	fscanf (fd, "%d", &H);
	fscanf (fd, "%d", &U);

	// citire inaltime si greutate gutui
	for (i = 0; i < N; i ++) {
		fscanf (fd, "%d", &gut[i].h);
		gut[i].h = ((gut[i].h - 1) / U + 1) * U;
		fscanf (fd, "%d", &gut[i].g);
	}
/*
	for (i = 0; i < N; i ++) {
		printf ("%d %d\n", gut[i].h, gut[i].g);
	}
*/
	fclose (fd);
}

void resolv ()
{
	int i;
	FILE *fd = fopen ("gutui.out", "w");
	
	qsort (gut, N, sizeof (gutui), comp);
	/*
	printf ("\n");
	for (i = 0; i < N; i ++)
		printf ("%d %d\n", gut[i].h, gut[i].g);*/
	
	i = 0;
	
	while (H > 0 && i < N) {
		if (gut[i].h <= H) {
			M = M + gut[i].g;
			H = H - U;
		}
		i ++;
	}
	
	fprintf (fd, "%d", M);
	fclose (fd);
}

int main ()
{
	read ("gutui.in");
	resolv ();	
	return 0;
}