#include <bits/stdc++.h>

using namespace std;

ifstream fin("lupu.in");
ofstream fout("lupu.out");

const int NMAX = 1e5+6;
struct oaie
{
    int dist, lana, mutari;
}w[NMAX];

bool cond(oaie A, oaie B)
{
    if(A.mutari == B.mutari)
        return A.lana > B.lana;
    return A.mutari < B.mutari;
}
int main()
{
    int n, x, l, i;

    fin >> n >> x >> l;

    for(i = 1; i <= n; ++i)
    {
        fin >> w[i].dist >> w[i].lana;
        w[i].mutari = (x - w[i].dist) / l;
    }

    sort(w+1, w+1+n, cond);

    int mutcurent = -1;
    long long sum = 0;

    for(i = 1; i <= n; ++i)
    {
        if(mutcurent != w[i].mutari)
            sum += w[i].lana, mutcurent = w[i].mutari;
    }

    fout << sum;

    return 0;
}