#include<stdio.h>
#include<algorithm>
#define MAXN 100000
struct Sheep
{
    int profit;
    int turns_survived;
};
bool cmp(Sheep,Sheep);
FILE*fin,*fout;
Sheep sheeps[MAXN+1];
int main()
{
    fin=fopen("lupu.in","r");
    fout=fopen("lupu.out","w");
    int N,X,L;
    fscanf(fin,"%d%d%d",&N,&X,&L);
    for(int i=1;i<=N;i++)
    {
        int initial_d,wool;
        fscanf(fin,"%d%d",&initial_d,&wool);
        sheeps[i].profit=wool;
        sheeps[i].turns_survived=(X-initial_d)/L;
        if(sheeps[i].turns_survived<0)
        {
            sheeps[i].turns_survived=0;
        }
    }
    std::sort(&sheeps[1],&sheeps[N+1],cmp);
    int ans=sheeps[1].profit;
    for(int i=2;i<=N;i++)
    {
        if(sheeps[i].turns_survived!=sheeps[i-1].turns_survived)
        {
            ans+=sheeps[i].profit;
        }
    }
    fprintf(fout,"%d",ans);
    fclose(fin);
    fclose(fout);
    return 0;
}
bool cmp(Sheep a,Sheep b)
{
    if(a.turns_survived==b.turns_survived)
    {
        return a.profit>b.profit;
    }
    return a.turns_survived<b.turns_survived;
}