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

unsigned long v[100000],s,x,n,l,i,ln,d,r;

int main()
{
	FILE *f;
	
	s=0;
	f=fopen("lupu.in","r");
	fscanf(f,"%lu%lu%lu",&n,&x,&l);
	for(i=0;i<n;i++)
		{
			fscanf(f,"%lu%lu",&d,&ln);
			if( d<=x)
			{
				r=(x-d)/l+1;
				if (ln>v[r])
				{
					s-=v[r];
					s+=ln;
					v[r]=ln;
				}
			}
		}	

	fclose(f);

	f=fopen("lupu.out","w");
	fprintf(f,"%lu",s);
	fclose(f);	

	return 0;
}