#include <iostream>
#include <fstream>
#include <queue>
#define Nmax 100000
using namespace std;
ifstream f("lupu.in");
ofstream g("lupu.out");
int n,Dmax,l,sum;
int lana[Nmax],t[Nmax],Tmax;
bool ins[Nmax];
priority_queue<int>pq;
int main()
{
    f >> n >> Dmax >> l;
    int x;
    for(int i=1;i<=n;i++){
        f >> x >> lana[i];

        t[i]=(Dmax-x)/l;
        Tmax=max(t[i],Tmax);
    }

    for(int i=Tmax;i>=0;i--)
    {
        for(int j=1;j<=n;j++)
            if(i==t[j] && ins[j]==0)
            {
                ins[j]=1;
                pq.push(lana[j]);
            }
            sum+=pq.top();
            pq.pop();
    }
    g << sum;

    return 0;
}