#include <fstream>
#include <algorithm>
#define Nmax 100005

using namespace std;

int N,X,L,len;

struct pereche
{
    int timp,lana;
    bool operator <(const pereche &A) const
    {
        return timp<A.timp;
    }
};
pereche v[Nmax];

inline void Read()
{
    int i,dist,lana,t;
    ifstream fin("lupu.in");
    fin>>N>>X>>L;
    for(i=1;i<=N;++i)
    {
        fin>>dist>>lana;
        t=(X-dist)/L;
        ++len;
        v[len].timp=t; v[len].lana=lana;
    }
    fin.close();
}

inline void Solve()
{
    int sol=0,poz,maxim,t;
    sort(v+1,v+len+1);
    poz=1;
    while(poz<=len)
    {
        maxim=0; t=v[poz].timp;
        while(v[poz].timp==t)
        {
            maxim=max(maxim, v[poz].lana);
            ++poz;
        }
        sol+=maxim;
    }
    ofstream fout("lupu.out");
    fout<<sol<<"\n";
    fout.close();
}

int main()
{
    Read();
    Solve();
    return 0;
}