#include <stdio.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h> 
#include <algorithm>
#include <vector>
#define MAXX 100001
using namespace std;
typedef struct date {
	uint32_t a;
	uint32_t b;
	} date;
	
vector<date> in;
date out[MAXX];

bool comp(date one, date two)
{
	return one.a>two.a;
}

int main () {
	
	FILE *f,*g;
	f=fopen("gutui.in","r");
	g=fopen("gutui.out","w");
	uint32_t n,h,u; 
	fscanf (f, "%d %d %d",&n,&h,&u);
	uint32_t i,j,x,y,pozmin;
	date aux;
	
	uint32_t gmax=0;
	
	for (i=0;i<n;i++)
	{
		fscanf (f, "%d %d",&x,&y);	
		aux.a=x;
		aux.b=y;
		in.push_back(aux);
	}
	
	sort(in.begin(),in.end(),comp);
	
	uint32_t k = 0; 
	
	for (i = 0; i < n;i ++ )
		if (in[i].a <= h) {
			out[k].b = in[i].b;
			gmax += in[i].b; 
			if(h<u)			 
				h=0;
			else
				h -= u ; 
			k++;
		}
		else {
			pozmin=0;
			for (j=1;j<k;j++) {				
				if (out[j].b < out[pozmin].b ) 
					pozmin=j;
			}			
			if ( in[i].b > out[pozmin].b ) { 				
				gmax = gmax + in[i].b - out[pozmin].b;
				out[pozmin].b = in[i].b;
			}
		}
	fprintf(g, "%d\n",gmax);
	fclose(g);
	return 0;
}