#include<stdio.h>
//int max[];
unsigned long N=0, H=0, U=0, nr=0, i, j, a=0, b=0, suma=0, *max;
FILE *f, *g;
int main()
{
    f = fopen("gutui.in","r");
    g = fopen("gutui.out","w");
    fscanf(f,"%ul", &N);
    fscanf(f,"%ul", &H);
    fscanf(f,"%ul", &U);
    nr = H/U;
    max = (unsigned long*) calloc (nr,sizeof(unsigned long));
    for(i=0;i<nr;i++)
    {
          fscanf(f,"%ul", &a);  //a este inaltime initiala
          fscanf(f,"%ul", &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,"%ul", suma);
    free (max);
    fclose(f);
    fclose(g);
    return 0;
}