#include <fstream>
#include <algorithm>
using namespace std;

ifstream is("lupu.in");
ofstream os("lupu.out");

int N, X, L;
int x, y;
int d, sol;

struct oaie{
    int dis, lana;
};

oaie o[100001];

bool CMP(const oaie &a1, const oaie &a2)
{
    if ( a1.dis != a2.dis )
        return a1.dis > a2.dis;
    else
        return a1.lana > a2.lana;
}

int main()
{
    is >> N >> X >> L;
    for (int i = 1; i <= N; ++i)
    {
        is >> x >> y;
        o[i].dis = (X-x)/L;
        o[i].lana = y;
    }

    sort(o+1, o+N+1, CMP);

    for (int i = 1; i <= N; ++i)
    {
        if (d != o[i].dis)
            sol += o[i].lana;
        d = o[i].dis;
    }

    os << sol;

    is.close();
    os.close();
    return 0;
}