#include<stdio.h>
#include<malloc.h>

typedef struct {
	unsigned int inaltime;
	unsigned int greutate;
	} gutuie;

//interschimba 2 elemente din vectorul de gutui
void swap(gutuie *a, gutuie *b) {
	gutuie aux;
	aux=*a;
	*a=*b;
	*b=aux;
}

//auxiliar pentru functia de sortare quicksort
int choose_pivot(int i, int j) {
	return ((i+j)/2);
}

//sorteaza descrescator in functie de greutate in vectorul de gutui
void qsort(gutuie *g, int m, int n) {	
	int key,i,j,k;
	if (m<n)
		{
			k=choose_pivot(m,n);
			swap(&g[m],&g[k]);
			key=g[m].greutate;
			i=m+1;
			j=n;
			while (i<=j)
				{
				while ((i<=n)&&(g[i].greutate>=key))
					i++;
				while ((j>=m) &&(g[j].greutate<key))
					j--;
				if (i<j)
					swap(&g[i],&g[j]);
				}
			swap(&g[m],&g[j]);
			qsort(g,m,j-1);
			qsort(g,j+1,n);
		}
	}
	
int main() {
	//DECLARARI VARIABILE
	unsigned int n,h,u,i,gt=0,cnt=0,j,localizare=0;
	FILE *in=fopen("gutui.in","r");
	FILE *out=fopen("gutui.out","w");
	
	fscanf(in,"%d",&n);
	
	//ALOCARI DE MEMORIE
	gutuie *g=(gutuie*)malloc(n*sizeof(gutuie));
	unsigned int *ord=(unsigned int*)malloc(n*sizeof(unsigned int));
	unsigned int *maxime=(unsigned int*)malloc(n*sizeof(unsigned int));
    unsigned int *nrg=(unsigned int*)malloc(n*sizeof(unsigned int));
	
	//CITIRE DIN FISIER SI COMPLETARE CAMPURI GUTUI	
	fscanf(in,"%u%u",&h,&u);
	for (i=0;i<n;i++)
		fscanf(in,"%u%u",&g[i].inaltime,&g[i].greutate);
	/*
	for (i=0;i<n;i++)
		printf("%d %d\n",g[i].inaltime,g[i].greutate);
	printf("\n");	
	*/
	qsort(g,0,n-1);
	/*
	for (i=0;i<n;i++)
		printf("%d %d\n",g[i].inaltime,g[i].greutate);
	printf("\n");
	*/
	//formez vectorul ord	
	for (i=0;i<n;i++) {
	//	if (g[i].inaltime>h)
	//		ord[i]=-1;
	//	else
			ord[i]=(h-g[i].inaltime)/u;
	}
		
	maxime[0]=nrg[0]=ord[0];
	
	gt=g[0].greutate;		
		
	for (i=1;i<n;i++) 
		//if (ord[i]!=-1) {
			{
				if (ord[i]>maxime[cnt]) {
					maxime[++cnt]=ord[i];
					nrg[cnt]=maxime[cnt]-maxime[cnt-1];
					gt+=g[i].greutate;
					nrg[cnt]-=2;
					}
				else {
					//localizare=-1;
					for (j=0;j<=cnt;j++) {
						if (ord[i]<=maxime[j]) {localizare=j;break;}
						}
					//while (localizare>=0) {
					for (;;) {
						if (nrg[localizare]>0) {
							gt+=g[i].greutate;
							nrg[localizare]-=2;
							break;
						}
						else
							{
								if (localizare==0) break;
								localizare--;
							}
					}
								
					}
				}
//			}
		
	fprintf(out,"%u\n",gt);		
	
return 0;
}