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

unsigned long long i,j,d,l,n,rez=0;
set<int> heap[100001];
struct oite
{
    unsigned long long dist,lana,ult;
};
oite a[100001];
bool cmp(oite a,oite b)
{
    if(a.ult==b.ult)
    return a.lana>b.lana;
    return a.ult<b.ult;
}
int main()
{
    ifstream f("lupu.in");
    ofstream g("lupu.out");
    f>>n>>d>>l;
    for(i=1;i<=n;++i)
    {
        f>>a[i].dist>>a[i].lana;
        a[i].ult=(d-a[i].dist)/l+1;
    }
    sort(a+1,a+n+1,cmp);
    for(i=1;i<=n;++i)
    if(a[i].ult!=a[i-1].ult)
    rez+=a[i].lana;
    g<<rez<<"\n";
    return 0;
}