#include <stdio.h>
#include <stdlib.h>
int max(int v[],int n){
    int i,max;
    max=0;
    for(i=0;i<n;i++)
    if (v[i]>max) max=v[i];
    return max;
}
int main(){
    int i,n,h,u,x,m,s;
    int *in, *gr,*v;
    FILE *f=fopen("gutui.in","r");
    FILE *g=fopen("gutui.out","w");
    
    fscanf(f,"%d%d%d",&n,&h,&u);
    in=(int*)malloc(n*sizeof(int));
    gr=(int*)malloc(n*sizeof(int));
    v=(int*)malloc(n*sizeof(int));
    
    for(i=0;i<n;i++){
    fscanf(f,"%d%d",&in[i],&gr[i]);

}
 x=max(in,n);
// printf("%d",x);
 s=0;
// printf("%d",max(gr,n));
    while(x>0){
               m=0;
               for(i=0;i<n;i++)
               if((in[i]>=x-u) &&(in[i]<=x)) {v[m]=gr[i];
                                           m++;
                                           }
               s=s+max(v,m);
               
               x=x-u;
               }
    fprintf(g,"%d",s);
 /*  for(i=0; i<n;i++){
    fprintf(g,"%d %d", *(in+i),*(gr+i));
    fprintf(g,"\n");
}*/
    
    fclose(f);
    fclose(g);
 //   getchar();
    return 0;
}