#include <stdio.h>
#include <malloc.h>

const char *fin="gutui.in";
const char *fout="gutui.out";

int N,H,U,GG;
int *pg, *ph;

// Functie pentru citire si validare numarului de gutui N

void readn()
{
     FILE *f;
     f=fopen(fin,"r");
     fscanf(f,"%d %d %d",&N,&H,&U);
     fclose(f);
     
     }

// Functie pentru citirea din fisierul gutui.in a vectorilor inaltimilor si
// greutatilor 

void readf(int *pg,int *ph)
{
     FILE *f;
     int i,j;
     f=fopen(fin,"r");
     fscanf(f,"%d %d %d",&N,&i,&j);
     for(i=0;i<N;i++)
     fscanf(f,"%d %d",ph+i,pg+i);
     fclose(f);
     }


// Functie pentru scrierea solutiei in fisierul gutui.out
 
void writef()
{
     FILE *f;
     f=fopen(fout,"w");
     fprintf(f,"%d",GG);
     fclose(f);
     } 

void q_sort(int pg[],int ph[], int st, int dr) //number=pg v=ph
{
  //int pivot,pivot1, l_hold, r_hold;
  int aux1, aux2, salvst, salvdr; 
  salvst=st;//l_hold = left;
  salvdr=dr;//r_hold = right;
  aux1=pg[st];//pivot = numbers[left];
  aux2=ph[st];//pivot1 = v[left];
  while(st<dr)//while (left < right)
  {
    while((pg[dr]>=aux1) && (st<dr))//while ((numbers[right] >= pivot) && (left < right))
      dr--;//right--;
    if(st != dr)//if (left != right)
    {
      pg[st]=pg[dr];//numbers[left] = numbers[right];
      ph[st]=ph[dr];//v[left] = v[right];
      st--;//left++;
    }
    while((pg[st]<=aux1)&&(st<dr))//while ((numbers[left] <= pivot) && (left < right)) 
      st--;//left++;
    if(st != dr)//if (left != right)
    {
      pg[dr]=pg[st];//numbers[right] = numbers[left];
      ph[dr]=ph[st];//v[right] = v[left];
      dr--;//right--;
    }
  }
  pg[st]=aux1;//numbers[left] = pivot;
  ph[st]=aux2;//v[left] = pivot1;
  aux1=st;//pivot = left;
  aux2=st;//pivot1 = left;
  st=salvst;//left = l_hold;
  dr=salvdr;//right = r_hold;
  if(st<aux1)//if (left < pivot)
    q_sort(pg,ph,st,aux1-1);//q_sort(numbers,v, left, pivot-1);
  if(dr>aux1)//if (right > pivot)
    q_sort(pg,ph,aux1+1,dr);//q_sort(numbers,v, pivot+1, right);
}
 
// Initializare vector la adresa p cu 0
void init(int *p)
{
     int i;
     for(i=0;i<N;i++)
     *(p+i)=0;
     }

int max(int v[], int n, int poz)
{
    int i;
    for(i=0; i<poz; i++)
    if(v[poz-i-1]==0) break;
    return poz-i-1;

}

// Functie pentru constructia vectorului nivelelor
// gutuilor 
void nivele(int *ph, int *nivel)
{   
    int i,*v;
    v=(int *)malloc(N*sizeof(int));
    for(i=0;i<N;i++)
    *(v+i)=0;
    for(i=N-1; i>=0; i--)
    {
    *(nivel+i)=(H+U-*(ph+i))/U;
    if(*(nivel+i) < 1) break;
    if(*(v +( *(nivel+i)-1)) ==0)
    *(v + (*(nivel+i)-1))=1;
    else 
    {
    *(nivel+i)=1+ max(v,N,*(nivel+i)-1);
    *(v+ (*(nivel+i)-1)) = 1;
    }
     
     }
}
 
// Functie pentru culegere gutui
int culeg(int *p, int *vmase)
{
    int i,masa;
    for(masa=0,i=0;i<N;i++)
    if(*(p+i)>0)
    masa+=*(vmase+i);
    return masa;
}


// n = numar de gutui din copac
// H = inaltimea la care poate ajunge culegatorul
// U = inaltimea cu care se ridica crengile dupa culegerea unei gutui
// vg = pointer catre vectorul maselor gutuilor
// vh = pointer catre vectorul inaltimilor la care se afla initial gutuile
// GG = masa totala a gutuilor culese
 
void afis(int *p, int n, char c)
{
     int i;
     for(i=0;i<n;i++)
     printf(" %c [ %d ] = %d \n",c,i,*(p+i));
     }
              
int main()
{
    int *nivel;
    readn();
    ph=(int *)malloc(N*sizeof(int));
    pg=(int *)malloc(N*sizeof(int));
    nivel=(int *)malloc(N*sizeof(int));
    readf(pg,ph);
    q_sort(pg,ph, 0, N - 1);
    init(nivel);
    nivele(ph,nivel);
    GG=culeg(nivel,pg);
    writef();
    return 0;
}