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

int main(){
	long a,b,N,H,U,lvl,i,s[100000],sum,j,b1;
	FILE *f=fopen("gutui.in","r");
	FILE *g=fopen("gutui.out","w");
	fscanf(f,"%ld %ld %ld",&N,&H,&U);
	lvl=H/U+1;
	sum=0;
	for(i=0;i<N;i++){	
		fscanf(f,"%ld %ld",&a,&b);
		j=(H-a)/U;
		//if(s[j]==0){
		//	s[j]=b;
		//}
		//else{
			while(j>=0){
				if(s[j]==0){
					s[j]=b;sum=sum+b;
					j=-1;
				}
				else 	{
					if(s[j]<b) {
						b1=s[j];
						s[j]=b;
						b=b1;sum=sum+s[j]-b;
						}
				}
				j--;
			}
		//}
	}
	
	//sum=0;
	//for(i=0;i<lvl;i++)
	//	sum=sum+s[i];
	fprintf(g,"%ld",sum);
	return 0;
}