#include <bits/stdc++.h>

using namespace std;

#define TITLE "lupu"

ifstream f (TITLE".in");
ofstream g (TITLE".out");

int main()
{
    int n,x,l;
    f>>n>>x>>l;
    priority_queue<pair<int,int>> PQ;
    for(int i=1;i<=n; i++)
    {
        int a,b;
        f>>a>>b;
        PQ.push({b,(x-a)/l+1});
    }
    int Ans=0;
    for(int i=1; !PQ.empty(); PQ.pop())
        {
            if(PQ.top().second>=i)
            {
                i++;
            Ans+=PQ.top().first;
        }
        }
    g<<Ans;
    return 0;
}