#include <stdlib.h>
#include <stdio.h>
#define N_MAX  10000

typedef struct{
	int h;
	int g;
}gutuie;



void Sort_Shell (gutuie v[], int dim){
	int i, pas, inv;
	gutuie a;
	pas = dim;
	while (pas >1 )
		{
		pas=pas/2 ;	
		do
			{
			inv=0 ; 	/* fals */		
			for (i=0; i < dim-pas; i++)
				{			
				if (v[i].g < v[i+pas].g)		//sortare descresactoare a greutatilor gutuilor
					{
					a=v[i+pas];
					v[i+pas]=v[i];
					v[i]=a;
					inv=1;		
				
					}
				}
			} while (inv);
		}
}

int main(){
gutuie sir[100000];
int i;
FILE *fp=fopen("gutui.in","r");
FILE *fp1=fopen("gutui.out","w");
char s[80];
fgets(s,80,fp);

char *sep=" ";
int N=atoi(strtok (s,sep));

int H=atoi(strtok (0,sep));

int U=atoi(strtok (0,sep));

int n=0,m;
while ( fgets(s,80,fp) != NULL ){
	sir[n].h=atoi(strtok (s,sep));
	sir[n].g=atoi(strtok (0,sep));

	n++;
}//end while

fclose (fp);
int g=0;

Sort_Shell(sir,N);
int inal=0;
int pas=1;


int a[H/U];
for (i=0; i<H/U; i++)
	a[i]=0;
for( i=0; i<N;i++){
	n=(H-sir[i].h)/U;
	m=n;
	while ((a[m]==1) && (m!=0))
		m--;
	if (a[m]==0)
		a[m]=1;	
	
}
for (i=0; i<H/U; i++){
	
	if (a[i]==1)
		g=g+sir[i].g;
}

fprintf(fp1,"%d",g);
fclose(fp1);
}