#include<conio.h>
#include<stdio.h>
//int max[];
int N=0, H=0, U=1, nr=0, i, j, a=0, b=0, suma=0, *max;
FILE *f, *g;
int main()
{
    f = fopen("gutui.in.txt","r");
    if(!f) {printf("eroare f"); return 1;}
    g = fopen("gutui.out.txt","w");
    if(!f) {printf("eroare g"); return 2;}
    fscanf(f,"%i", &N);
    fscanf(f,"%i", &H);
    fscanf(f,"%i", &U);
    nr = H/U;
    max = (int*) calloc (nr,sizeof(int));
    for(i=0;i<nr;i++)
    {
          fscanf(f,"%i", &a);  //a este inaltime initiala
          fscanf(f,"%i", &b);  //b este greutatea
          j= nr - a/U;          //j indica ordinea de evaluare
          if(b > max[j-1]) max[j-1] = b;
    }
    for(i=0;i<nr;i++) suma += max[i];
    fprintf(g,"%i", suma);
    printf("%i ", suma);
    free (max);
    fclose(f);
    fclose(g);
    getch();
    return 0;
}