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

int main(){
	long a,b,N,H,U,lvl,i,s[100000],sum,j,lvlm,b1,b11;
	FILE *f=fopen("gutui.in","r");
	FILE *g=fopen("gutui.out","w");
	fscanf(f,"%ld %ld %ld",&N,&H,&U);
	lvl=H/U;
	for(i=0;i<N;i++){	
		fscanf(f,"%ld %ld",&a,&b);
		lvlm=(H-a)/U;
		b1=b;
		j=lvlm;
		while(j>=0){
			if(s[j]==0){
				s[j]=b1;
				j=0;
				}
			else 	{
				if(s[j]<b1) {
					b11=s[j];
					s[j]=b1;
					b1=b11;
					j++;
					}
				}
			j--;
		}
	}
	
	sum=0;
	for(i=0;i<lvl;i++)
		sum=sum+s[i];
	fprintf(g,"%ld",sum);
	return 0;
}