#include <fstream>
#include <map>
using namespace std;
ifstream fin("lupu.in");
ofstream fout("lupu.out");
int n,d,l,oaie,lana,sum,p;
map <int,int> a;
int main()
{
    fin>>n>>d>>l;
    for(int i=1;i<=n;i++)
    {
        fin>>oaie>>lana;
        if(oaie<d)
        {
            p=(d-oaie)/l;

            if(a[p]<lana)
            {
                sum-=a[p];
                a[p]=lana;
                sum+=a[p];
            }
        }
    }
    fout<<sum;
    return 0;
}